Stacked lens configuration

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astrofriend
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Joined: Mon Dec 31, 2018 2:28 am
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Stacked lens configuration

Post by astrofriend »

Hi,
I have started some macrophotographing, I will have this as a complement to astrophotographing. Astrophotographing needs clear sky and darkness, something that's not so easy to get today. Macrophotographing I can do indoors when bad weather.

Long time ago, before the digital cameras I did some macrophotographing with a reversed lens. Now I do that with a Canon 6D full frame camera and testing some lenses in reversed setup. I also do it with focus stacking.

You can see my first tests here:
http://www.astrofriend.eu/photography/m ... -test.html

They all look a bit soft, maybe vibrations.

After I had reading here at macro forum I understand if I want to go longer than 2x magnification it could be interesting to stacking lenses. The Sigma APO 150 mm f/2.8 is said to be a good lens for this and that is just what I have. I have ordered a couple of reverse rings to connect the Sigma lens to other shorter focal lenses.

The second stacked lens is planned to be somewhere between 24 to 50 mm to have a magnification around 3 to 5 times.

Has I understand it correct that it's best to keep the distances between the two stacked leneses as short as possiblie, or?

Today I move the object with a macro slider which is the normal way to focus when doing macro. A stepper motor controlled macro slider isn't cheap, maybe I can buy one later.

Now when testing I will try to use the focus motor in the Sigma lens but not sure if it works. It had felt better to focus the second lens and keep the long focal lens at infinity. But then I can't control it from the camera so easy.

/Lars
Best Regards
Lars

Homepage
http://www.astrofriend.eu/

JohnyM
Posts: 463
Joined: Tue Dec 24, 2013 7:02 am

Post by JohnyM »

Looks like diffraction blur to me. What aperture were you shooting at?


Distance between lenses is arguable. If you use both lenses focused on infinity, theoretically you could place them infinitely apart. Here is calc that can help you estimate:
https://www.edmundoptics.com/resources/ ... be-length/

Objective - front lens
NA - calculated from F stop
Tube lens entrance pupil - ROUGHLY, put a scale on your lens front glass. Then look at aperture blades and try to measure the hole.
Tube lens - rear lens

If you focus rear lens in macro range, greater the distance between lenses, bigger the magnification you'll get, also greater optical flaws. You'll hae to decide what you prefere. Perfection or usability.
Last edited by JohnyM on Mon Dec 31, 2018 5:57 am, edited 1 time in total.

astrofriend
Posts: 3
Joined: Mon Dec 31, 2018 2:28 am
Location: Sweden
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Post by astrofriend »

Hi,
Yes maybe that's the case, I used it at full aperture and both lenses I tested are very old, from 1960s I think.

What aperture do you reccomend in general? To big give softness and to low and reaching the diffraction limit.

I shall later test the Canon 50mm f/1.8, maybe much better optical quality. Just waiting for all the adapters I need.

When using that Canon lens for astronomy I set the aperture to f/4, then it's optimum between light through put and sharpness.

Thanks for the link.

/Lars
Best Regards
Lars

Homepage
http://www.astrofriend.eu/

Macrero
Posts: 1166
Joined: Thu Sep 01, 2011 8:17 am
Location: Valladolid , Spain

Post by Macrero »

When "stacking" two lenses, you are creating a new lens with an unpredictable behaviour. No method I am aware of to determine how good or bad the result will be, or how should you "configure it" in order to get optimal result, other than trial and error. Shorter distance between lenses = better coverage, but not = better "quality".

Best,

- Macrero
https://500px.com/macrero - Amateurs worry about equipment, Pros worry about money, Masters worry about Light

Troels
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Joined: Mon Feb 15, 2016 11:06 am
Location: Denmark, Engesvang
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Post by Troels »

Astrofriend,

Try doing a search on this site and you will find a lot of important information about "stacking lenses".

But don't use "stacking" as key word in your searching. That will lead you in a complete different direction. In this community it is normally called "combo lenses". All your questions and many more are answered in older posts. Lots of interesting readings.
Troels Holm, biologist (retired), environmentalist, amateur photographer.
Visit my Flickr albums

astrofriend
Posts: 3
Joined: Mon Dec 31, 2018 2:28 am
Location: Sweden
Contact:

Post by astrofriend »

Hi Macrero and Troels,
Thanks for the information. The adapters I have ordered in different sizes makes it very flexible how I connect it together. Then I can do experiements how to set it up for optimal performence.

I have checked others threads and I'm think I'm on the right way.

Combo lenses was a new word for me, always used stacked lenses.

Lars
Best Regards
Lars

Homepage
http://www.astrofriend.eu/

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