Microscope objective with tiny sensor.

[skrylten]

From another thread Rik mentioned the possibility to combine my Powershot SX50 (sensor size 6,17*4,55 mm, lens zoom 4,3-215 mm) with a microscope objective.
It sounds like a fun project if its not to costly ( 0,15 mm would cover the width of the sensor with a 40x objective ).
But after some thinking I got some questions.

1: Does it have to be an infinite objective, due to the fixed zoom lens ?
2: Could I settle with an objective that is not good enough on larger sensors, due to bad performance "off center" ?
3: If thats the case... Any suggestions for suitable objectives (10x,20x,40x) to get out of the Mitu/Nikon competion on ebay ?
4: Would it still be possible to let the camera do the focus steps (CHDK), or do I have to focus on infinity and use a rail ?
5: Should the objective be as close as possible to the zoom lens ?

Other thoughts from all the experienced members ?

Today I use the camera with Raynox lenses to id small bugs.

/Leif

[rjlittlefield]

From another thread Rik mentioned the possibility to combine my Powershot SX50 (sensor size 6,17*4,55 mm, lens zoom 4,3-215 mm) with a microscope objective.

I believe that mention is HERE.

1: Does it have to be an infinite objective, due to the fixed zoom lens ?

Yes. Using a finite objective in this situation invites softness. Even with the rear lens set to infinity focus, a finite objective would be forced to focus different from its design. Shifting focus of the rear lens to "closer" would make the problem even worse.

2: Could I settle with an objective that is not good enough on larger sensors, due to bad performance "off center" ?

Sensor size is not a strong issue here. If you use the objective's whole field, probably still you will not be stressing the resolution of your sensor. If you use less than the whole field, then the image will just get softer because you will be getting "empty magnification".

4: Would it still be possible to let the camera do the focus steps (CHDK), or do I have to focus on infinity and use a rail ?

At lower magnification, say 10X objective, you can do a lot by focusing the rear lens. See AF motor focusing with a microscope objective.

5: Should the objective be as close as possible to the zoom lens ?

Yes. Moving out will only make vignetting worse.

--Rik

[skrylten]

Rik: Thanks for all the answers.

One more question about the second answer:

Does this mean that it is better to use a 10x objective at less magnification (to use the objective´s whole field) than to use it at 10x and use the center of the field ?

[rjlittlefield]

Does this mean that it is better to use a 10x objective at less magnification (to use the objective´s whole field) than to use it at 10x and use the center of the field ?

In some sense yes. One good way to think about this is that the objective creates an image with limited resolution and limited width. If you zoom out too far then you don't cover the sensor so image quality degrades due to finite sensor resolution. But if you zoom in too far then you're throwing away available detail on the edges and not making up for it in the middle because there's no more there to see.

So, if you're just interested in capturing as much detail as possible with the objective -- with no particular subject in mind -- then your best approach is to just barely cover the sensor with the high quality image circle made by the objective.

However, as soon as you say "I want to take the best picture I can of this subject", then the best approach changes to filling the sensor with that subject. It's no problem if you have to throw away high quality image circle to do that. You're not interested in any of the stuff that's being thrown away, and by expanding the stuff you do care about to cover the sensor, you'll improve the captured quality of just that area.

--Rik

[skrylten]

Great explanation Rik !

Thanks again ...