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Film vs ccd question

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#1 imtl

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Posted 27 February 2021 - 09:36 PM

Maybe I should post this in Experienced DSO imaging or refractors but let's give it a go here first.

 

Does anyone know what is the difference in refractors optimized for imaging with film vs. more modern ones optimized for imaging with CCD/CMOS?

 

In both cases it is an apo triplet so simplify things.

 

Thanks!



#2 Midnight Dan

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Posted 27 February 2021 - 09:43 PM

I'll be interested to see the responses.  I've never heard of a refractor being optimized for film vs. CCD.  Can't imagine why there would be a difference. 

 

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-Dan



#3 imtl

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Posted 27 February 2021 - 09:50 PM

I guess because of CCD/CMOS sensors different spectral response?



#4 mashirts

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Posted 27 February 2021 - 09:57 PM

Orthographic film maybe?  No need to consider the red spectrum.



#5 copper280z

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Posted 27 February 2021 - 10:02 PM

I guess because of CCD/CMOS sensors different spectral response?


I don't think the spectral response is ALL that different. You can still find film data sheets online. Films like Ektar and E100 have significant Ha response, as it turns out.

My guess is that the scope designed around film MAY have a larger spot size, because I'm not sure film has the spatial resolution of a modern sensor. You might be able to do some analysis from the datasheet and from sensor specs.
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#6 TOMDEY

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Posted 28 February 2021 - 12:34 AM

The likelihood that they're actually different is right around zero --- which means they are fine for both.

 

Similarity: Broadband coatings for flat fold mirrors usually have designations for either normal incidence or 45o angle of incidence (90o fold). In actuality, the coatings are absolutely identical... and fine for either application. The film vs solid state detector designation tends to be the same concept. It makes you feel that you are getting something customized special, just for you. It's in no way deceptive because it performs to specifications.

 

On the other hand, there are indeed some specialty lenses and coatings that are optimized and built for one best application. e.g. The Lunt dedicated H-alpha eyepieces, which sport antireflection coatings with their minimum reflectivity right at that wavelength. I bought pairs of all of them.    Tom

 

[I was a coating engineer/scientist at B&L for twelve years.]

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#7 ngc7319_20

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Posted 28 February 2021 - 12:35 AM

Could also be related to "sensor" size.  Film sizes could run pretty large:  70mm, 6x7cm, 6x9cm, 4x5", 8x10", 16x20".    Mostly we don't see CCD/CMOS larger than about 35mm format.


Edited by ngc7319_20, 28 February 2021 - 12:35 AM.


#8 Der_Pit

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Posted 28 February 2021 - 10:01 AM

I guess similar as for photo lenses, the optical design was based on the typical grain size of the detector.  That used to be rather in the 24μ regime, so the less expensive glass had no reason to be able to deliver higher lines/mm resolution than what the film really could see.  Quite s different world if you have 4μ pixels.

But for expensive ("premium") equipment that mostly doesn't apply.  Good 'old' lenses are still excellent with modern detectors, and I'd assume most APOs fall in that category....



#9 Alex McConahay

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Posted 28 February 2021 - 11:11 AM

If I recall, I believe I was once told that "Film" in a 35 mm full frame was the equivalent of 35 Megapixels. I was told that maybe 20 years ago, when people were saying why Film could offer better resolution than digital detectors. Of course, digital detectors were only doing one to maybe twelve megapixels at the time. And, I would imagine Ektachrome had a much higher resolution than did Tri-X. So, I do not know where the 35 megapixels came from. And, of course, some of our cameras now exceed that 35 megapixel size. 

 

But, in all my years, I cannot recall seeing tubes optimized for digital versus film detectors.  

 

Alex


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#10 Midnight Dan

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Posted 28 February 2021 - 11:14 AM

Maybe I should post this in Experienced DSO imaging or refractors but let's give it a go here first.

 

Does anyone know what is the difference in refractors optimized for imaging with film vs. more modern ones optimized for imaging with CCD/CMOS?

 

In both cases it is an apo triplet so simplify things.

 

Thanks!

Perhaps you can provide some context.  Where have you heard anything about refractors optimized for film vs. digital sensors?

 

-Dan




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