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Mounting 2" Filter drawer behind lens
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PostPosted: Wed Aug 25, 2021 7:10 am    Post subject: Mounting 2" Filter drawer behind lens Reply with quote

I have a couple filters that I would like to use on wide angle lenses with huge front element.

Any drawbacks to mounting a filter drawer in between the lens and an APS-C Sony mirrorless camera?


Example filter drawer:

https://www.highpointscientific.com/zwo-m42-filter-drawer-2-fd-m42

Friends


PostPosted: Thu Aug 26, 2021 7:51 am    Post subject: Re: Mounting 2" Filter drawer behind lens Reply with quote

This is solved. Someone here actually answered a while back related to a similar topic of optical path and sensor hot mirrors. Unless I am missing something else.

Back focus of 1/3 glass thickness. Wink


Also here

https://optcorp.com/blogs/deep-sky-imaging/how-to-set-the-correct-back-focus


PostPosted: Sat Aug 28, 2021 9:57 am    Post subject: Reply with quote

Yes, indeed, it will cause some back focal issues due to the 1/3 filter thickness elongated optical path.
I have done that for UV photograph, which was not infinity, so worked pretty well back then...


PostPosted: Sat Aug 28, 2021 10:56 pm    Post subject: Reply with quote

Now I just need to find a model that works with the thick Baader filters, shallow, and does not obstruct the use of a Sony APS-C camera.

I would be tempted to try the Baader filter slider but most parts are out of stock and it seems like it might obstruct use of the camera.

I already noticed that the Baader 2" filters are about 1mm too thick for the Canon FD drop in (300mm, 400mm and 500mm). That's separate issue but I already have an approach for this. Does not include remounting the filter.


PostPosted: Thu Oct 14, 2021 3:27 pm    Post subject: Reply with quote

Still waiting for the Baader 2" filter sliders to re-stock. Been waiting several months. Every drawer that I have seen for sale doesn't work with the thicker Baader filters.

I don't want to re-mount the filter into a new ring or unmount it naked into a fixed slider. Decided to make a rapid prototype drawer that uses the Canon telephoto drop in filter holder.

The drawer itself is 19.5mm thick. It has M42x1mm on each side. Most drawers are M42x0.75mm. I think that is T2. Or they are custom to the camera sometimes M48 on the front. Having M42x1 allows me to fix any type of camera mount on the rear and a focus helical on the front.

Right now I have it connected to a 15-26mm macro focus helical. That brings the total length of the system to 35.5mm which is slightly longer than the fixed size Fotodiox M42 to Sony E-mount of 28.7mm. This is just the prototype. It still needs flocking.

I can probably reduce the overall length to match the standard M42 to Sony E-mount adapter. I only need to find 6.8mm. I can recess the male M42 in the rear so the Sony E-mount slim adapter fits inside and there is some space inside the chamber as well as making the female M42 in the front a little shorter. I also have a super small focus helical that goes down to 9.9mm which I could use. Actually, that would get me where I need to be for infinity with M42 lenses.

As far as adapting Exakta or Nikon F-mount I would need another 2.5 - 3mm. I think that it can be done and reach infinity on those mounts with some creative thinking. Or just not use the focus helical for lenses that don't require that like telephoto or fisheye.


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