Mid-Format DOF Adapter

mvansomeren

mvansomeren

Well-known member
I've been working on a mid format adapter for a couple of months. I started with a vibrating GG version but didn't like the results (and the annoying buzzing) so I decided to try my hand at a spinning GG version.

The GG is real glass that I hand cut from a large square focus screen I got on eBay.

In my first version I used a $5 macro lens for the achromat. Although the DOF part worked pretty well, there was a ton of CA and edge-to-edge sharpness left a lot to be desired. After some good advice from folks on this forum and others, I purchased the achromat used on the SGpro. The difference was night and day!

I like the fact that I have a larger GG surface to focus on as opposed to a 35mm adapter. However, it is larger and heavier. My next project will be to build a more compact version.

This version has a Mamiya lens mount and excluding the lens and achromat, cost about $60 in parts to build.

Here are pictures of the adapter and the test video using the new achromat:

http://exposureroom.com/70mmtest

(you can also see the video shot with the cheap achromat to see the difference located on the same site)
 

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Whoa. This looks interesting.

What is the advantage of going medium format?

Since the GG is larger, you would need a longer focal length to achieve the same FOV right?

This would result in EVEN shallower DoF.

Are there other differences? Since the lenses are presumably larger, do they come with faster apertures?
 
I'm by no way an expert on lenses and I'm sure others can provide you a better answer than I can. I have seen the same speeds available for these lenses as for 35mm lenses so it may be relative to the size of the lens.

The DOF is pretty shallow but not ever owning a 35mm adapter, I don't have anything to compare it to. There are a couple of others on this forum who have built mid format adapters and might have more insight.

To my way of thinking, it would seem better to start with a larger projection than to have to zoom in to enlarge a smaller one. I may be totally off base with that...

Also, there is someone on this forum that manufactures a retail vibrating mid format adapter but never posted any un compressed footage to check out. I got tired of waiting so I decided to make my own. I didn't like the resuts so I tried spinning GG instead and that made a big difference. I am pretty pleased with the picture so far.
 
mvansomeren said:
I'm by no way an expert on lenses and I'm sure others can provide you a better answer than I can. I have seen the same speeds available for these lenses as for 35mm lenses so it may be relative to the size of the lens.

The DOF is pretty shallow but not ever owning a 35mm adapter, I don't have anything to compare it to. There are a couple of others on this forum who have built mid format adapters and might have more insight.

To my way of thinking, it would seem better to start with a larger projection than to have to zoom in to enlarge a smaller one. I may be totally off base with that...

Also, there is someone on this forum that manufactures a retail vibrating mid format adapter but never posted any un compressed footage to check out. I got tired of waiting so I decided to make my own. I didn't like the resuts so I tried spinning GG instead and that made a big difference. I am pretty pleased with the picture so far.
Click to expand...

Oh ok. If you plan on zooming into a medium format past its dimensions, you may end up with the same focal length, not needing to add a longer lens.

This makes sense. The DoF would remain the same (as 35mm) if you did that.

Makes total sense.
 
It just dawned on me that the video says I used a 50mm lens when in fact it was an 80mm lens. Maybe that is what was confusing.
 
Nah, but I understand. If you want me to explain what I was thinking I can. I think I am fully caught up right now. There should be little difference between your adapter and the 35mm adapters, in regards to depth of field etc. You just have a cushier area outside frame before vignetting and other side effects present themselves. Only if you were to zoom out and be looking at a larger section of GG, would you require a longer lens for the equivalent FoV and therefore lose DoF.

Lol.
 
Winston Vargas already built one and is selling thru Adorama. Very soon it will be the first dual adapter allowing you to use both 35mm and mid format lenses. Although he is still learning how to compress the h264 file he posted some stuff in Vimeo done with the adapter and the HV20. I lent him my HVX last week so he would be able shoot some more footage with it.

www.vimeo.com/1611856
 
John,

You're always posting about and advertising for Winston. You should know that Winston is not the first to make a dual adapter. If you search the forum, you'll see that someone else created a dual 35mm and mid format spinning GG DOF adapter many months ago. In fact, he's the person that helped me with my CA issues by telling me how he solved his.

Winston is the person I was referring to that is sellng a retail mid format vibrating adapter. As I mentioned earlier, after numerous requests from many on this forum, up until 6 days ago, he had yet to post downloadable HD 720p footage so we could see how the adapter works without the compression artifacts. Not having that footage is what spurred me on to build my own, and, finding the vibrating version I built (with the same GG dimensions that Winston uses) produced a less than stellar image, I built the spinning GG version which turned out much better.

This thread is not about selling a mid format adapter. It's just about my project and sharing what i've learned. No offense, but posting an advertisment for Winston is, in my opinion, out of place in this thread. But, if you want to talk about the technical aspects of a mid format adapter, offer constructive suggestions for improvement, etc., then you're more than welcome.
 
I apolagize for that. Winston had been lagging on showing sample work and I have encouraged him to show more stuff done with it. I lent him my HVX so he can do something other than the HV20 he has done. The truth is the adapter works extremely well with the vibrating GG. It is incredibly sharp and you dont need the achromat to use it. There are a lot of people who have bought it and keep telling him how good it works but he tells me they haven't sent him any footage for him to show. The only one that did was Monstar Films.
Again I am sorry. After I posted I realized I made a mistake doing it. One last thing that may be of interest to you as far as knowledge is that the secret to Winstons adapter is the quality of the ground glass. He is paying a heck of a lot of money, IMO, but it makes a big difference.
Good luck to you on your project.
 
Just a question about mid-format:

Isn't the low resolution on the DV-HDV format-cameras not enough for make it in to an advantage with the high resolution available with mid-format lenses etc? Like Hasselblad H3D cameras, the resolution surpasses other digital cameras by far. But in this field for DV-HDV cameras it won't be to an advantage…

You have certaily made a great adapter, but I just want to know if the market is in a need for the technology?

Thanks
 
David Odell said:
Just a question about mid-format:

Isn't the low resolution on the DV-HDV format-cameras not enough for make it in to an advantage with the high resolution available with mid-format lenses etc? Like Hasselblad H3D cameras, the resolution surpasses other digital cameras by far. But in this field for DV-HDV cameras it won't be to an advantage…

You have certaily made a great adapter, but I just want to know if the market is in a need for the technology?

Thanks
Click to expand...

I am not an expert on medium-format lenses, but I can help answer what a medium format adapter could present.

This is my stab at what I think medium format could offer. You'd best wait to hear from Mvansomeren.

First of all, when it comes to depth of field, the larger the format the less the depth of field. Now, the format size isn't what is exactly effecting depth of field but rather the lens length.

Take 35mm and 16mm film for example. A 25mm lens on a 16mm film camera, is equal to a 50mm lens on a 35mm film camera. This is because the 35mm film camera is about twice the size of 16mm, so in order to get the same Field of View, one needs to double the focal length. Longer focal lengths make the depth of field more shallow.

So if one was to use the medium format lens adapter, and zoom in just enough to get past the adapter and minimize vignetting, one would be looking at a much larger area of ground glass then compared to the 35mm adapter user. This would require a longer lens to get that medium shot, or a longer lens to get that close up, etc. The longer lens would lessen depth of field.

But from talking with Mvansomeren, it seems he was not taking advantage of the possible 'shallower' depth of field but rather zooming even further past what I described and returning close to the Field of View otherwise found on 35mm adapters.

You may ask what the advantage is, if he is just going to zoom to about the same FoV as 35mm. Well, when we zoom into our ground glasses, we are often just barely past the adapter and there is still some faint vignetting, edge to edge sharpness issues, etc. Since his adapter allows him to zoom in much further past the edges of the GG, he is creating a large safety area. There will be less chances of seeing an adapter part, vignetting, etc.

Not knowing alot about medium format, I would venture to say the lenses used on medium format may be able to resolve more detail?

A very doubtful but theoretically based advantage: The HVX lens loses light as it zooms in. The lens starts at a f/1.7 lens, and closes down the more you zoom. I doubt the amount of zooming in you save from a medium format adapter would be enough to gain back some lens sensitivity, but it hasn't been tested yet. In theory, if you can zoom out further on medium format adapter you could gain a small and probably unnoticeable amount of sensitivity.

I'll wait for Mvansomeren to weigh in, but that was my view on it.
 
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Ryan,

You certainly are correct about the lenses. In order to get the same FOV as a 50mm, 35mm format lens, you need an 80mm lens on the medium format.

Now as far as zooming in, it does give you a nice safety area. I zoom in just past where I see some light fall off on the edges. However, I don't believe that I'm zooming is as far as I would on a 35mm adapter. One of the things that drives me crazy is when I see video from 35mm adapters and there is vignetting, so I zoom in just past that.

I have read in other forums, though I don't know if it is true, that when you zoom in close to fully, you loose some sharpness. That and the vignetting is why I decided to try a medium format adapter rather than a 35mm.

This was just something I wanted to try to see if I could get reasonable results. Plus, I learned a great deal about the mechanics of DOF adapters. I even learned how to cut a circle out of glass! LOL

It was and coninues to be a fun project. I want to try and build a more compact version and possible make some teaks to make it better, like adjustable back focus, etc.
 
This idea sounds really neat. How is the light loss on medium format compared to 35mm? About the same? I'm thinking that because of the larger GG perhaps a little less light would be loss.
 
I don't have a 35mm adapter to compare but I suppose it depends more on the GG used, lens and whether or not a condenser is used ratther than what format it is.

Anyone who knows the real answer, feel free to step in here.
 
mvansomeren said:
John,

You're always posting about and advertising for Winston. You should know that Winston is not the first to make a dual adapter.
Click to expand...


http://www.dvxuser.com/V6/showthread.php?t=121773&

I´m just saying :D


Regarding DOF. I only use Zeiss medium format lenses on the LEX and there is no DOF difference between them and a 35mm lens.

I think it´s because you are using the sweet spot of the medium lens only.


Frank
 
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mvansomeren said:
However, I don't believe that I'm zooming is as far as I would on a 35mm adapter. One of the things that drives me crazy is when I see video from 35mm adapters and there is vignetting, so I zoom in just past that.

I have read in other forums, though I don't know if it is true, that when you zoom in close to fully, you loose some sharpness. That and the vignetting is why I decided to try a medium format adapter rather than a 35mm.

This was just something I wanted to try to see if I could get reasonable results. Plus, I learned a great deal about the mechanics of DOF adapters. I even learned how to cut a circle out of glass! LOL

It was and coninues to be a fun project. I want to try and build a more compact version and possible make some teaks to make it better, like adjustable back focus, etc.
Click to expand...

If you aren't zooming in far enough to match 35mm Field of View, then you are going to have a wider field of view needing longer lenses to match the equivalent composition.

You my friend are going to have shallower DoF, then 35mm adapters... and that's downright shallow!! I feel really bad for your 1st ac. lol.

Of course you can always deepen the DoF by doing a multitude of things. I'm stating that at wide open, you will naturally be on a shallower DoF scale.
 
Postmaster said:
http://www.dvxuser.com/V6/showthread.php?t=121773&

I´m just saying :D


Regarding DOF. I only use Zeiss medium format lenses on the LEX and there is no DOF difference between them and a 35mm lens.

I think it´s because you are using the sweet spot of the medium lens only.


Frank
Click to expand...

That is because the lenses aren't what makes the difference. It is the size of the GG/format.

He can see a much larger picture because his ground glass is larger. Therefore he is required to use longer lenses to get the same FoV. The longer lens length is what creates the shallow DoF.

Unless his Ground Glass is the same size as 35mm adapters (which I thought it wasn't) would it be the exact same as 35mm adapters. The lens type doesn't matter, the lens length does. He needs a longer length to see what you see with a shorter one.
 
Which, if I'm understanding you correctly, is why I'm using an 80mm mid format lens to approximate the FOV of a 50mm, 35mm lens.
 
I'll try to get some additional testing done this weekend before I head out of town. I need to purchase some additional mid format lenses as well.
 
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