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Problems with Ektar 100 (or Yashica Mat)

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#1 balazs.benei

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Posted 07 September 2021 - 02:59 PM

Hi guys, I need your kind help.

 

I've tried to shoot astro target on Ektar 100 with Yashica Mat 124 and it did not turn out well. I've had several problems:

 

- Exposure - I've tried different exposures and f stops but neither of them are acceptable. For example, this shot was 40 minutes long at f/3.5. I do not know what went wrong but this is too dark for me, the sky quality was around Bortle 2-3. Scanning was made by the lab.

Ektar fail
 
- Guiding - Other big problem for the second shot was the guiding. This was 60 minutes long at f/4.5, same flat crap as the first one but guiding failed as well and I don't know why. The guiding star was continuously in the center of frame but the whole image rotated somehow around one point (which is not Polaris). My guess is that PA for this attempt was not so accurate as for the first one but meanwhile PHD2 did the guiding well, the field rotated around the guiding star. Or do you have any other ideas how to solve this guiding failure?
Guiding fail

 

 



#2 Todd N

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Posted 07 September 2021 - 08:26 PM

Well, Ektar 100 looks like a not so great film for astrophotography which is what I recall about it going back so many years.  I've spent most of this year playing around with other B&W films that I probably shouldn't have and don't have good results to share. It's just the nature of the business. You shouldn't necessarily expect perfect results. You can play around with adjusting color channels to improve the image which is common even with film.  You might try some other films like Kodak Porta. I don't know if the 160 has extended red sensitivity but I think the 400 and 800 do. Another approach is to do several shorter exposures with faster film and then align and stack them in post processing to improve signal to noise and lessen grain: Three to four 10, 15 or 20 minute exposures. This has the advantage of lessoning guiding requirements, being able  to eliminate film anomalies from one frame to another(dust, scratches in postprocessing) and not wasting imaging time when reciprocity starts to take over. 

 

You got real significant field rotation. Your polar alignment was too far off.


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#3 Eric P

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Posted 08 September 2021 - 07:59 AM

I tried the new E100 last year with a Schmidt Camera (202mm @ f1.5) and was able to get a decent response though not as good as the old E200.  Could this be more of an issue with the limited aperture of the Yashica Mat vs the E100?


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#4 Eric P

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Posted 08 September 2021 - 08:02 AM

Well, Ektar 100 looks like a not so great film for astrophotography which is what I recall about it going back so many years.  I've spent most of this year playing around with other B&W films that I probably shouldn't have and don't have good results to share. It's just the nature of the business. You shouldn't necessarily expect perfect results. You can play around with adjusting color channels to improve the image which is common even with film.  You might try some other films like Kodak Porta. I don't know if the 160 has extended red sensitivity but I think the 400 and 800 do. Another approach is to do several shorter exposures with faster film and then align and stack them in post processing to improve signal to noise and lessen grain: Three to four 10, 15 or 20 minute exposures. This has the advantage of lessoning guiding requirements, being able  to eliminate film anomalies from one frame to another(dust, scratches in postprocessing) and not wasting imaging time when reciprocity starts to take over. 

 

You got real significant field rotation. Your polar alignment was too far off.

I tried Portra 160 but my exposure had a significant green cast after an hour's exposure (Hasselblad 50mm @ F4).  Hopefully I get a chance to revisit Portra with the Schmidt Camera.


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#5 Todd N

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Posted 08 September 2021 - 09:29 AM

I tried Portra 160 but my exposure had a significant green cast after an hour's exposure (Hasselblad 50mm @ F4).  Hopefully I get a chance to revisit Portra with the Schmidt Camera.

From the Porta 160 techpub, it's not a good choice for H-alpha and I can see why green dominated in the image. Look at the green layer in the Spectral Sensitivity Curves. The green has huge crossover into the blue, no wonder.

 

https://imaging.koda..._portra_160.pdf

 

I bought a couple of Cinestill 50 but I have never tried it and they are long expired. This is rebranded Kodak Color film and the spectral response looks ideal. There is also a 800. It would be nice for someone to try it out especially on a schmidt. 

 

https://www.freestyl...0-35mm-x-36-exp.

 

https://www.kodak.co...80929-SP_EN.pdf


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#6 Michal1

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Posted 09 September 2021 - 06:34 AM

The first image appears overexposed. It is better to judge this from looking directly at the film. Maybe your lab made the background that light as an digital adjustment after the scanning. Some scanners do that automatically. Then you would have to ask the staff of your lab to pay special attention to when scanning your images. I ended up by using the services of labs that specialize on digitizing films. The scanner of the lab in my town was simply not able to deliver nice results, even after many discussions with the staff.

 

The problem of the second image is most probably a poor polar alignment. What polar alignment method did you use? For 60 min shots you need a high precision of the alignment. I made the PARot program to address this issue: https://sourceforge....projects/parot/


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#7 Joe F Gafford

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Posted 09 September 2021 - 06:32 PM

The first image appears overexposed. It is better to judge this from looking directly at the film. Maybe your lab made the background that light as an digital adjustment after the scanning. Some scanners do that automatically. Then you would have to ask the staff of your lab to pay special attention to when scanning your images. I ended up by using the services of labs that specialize on digitizing films. The scanner of the lab in my town was simply not able to deliver nice results, even after many discussions with the staff.

 

The problem of the second image is most probably a poor polar alignment. What polar alignment method did you use? For 60 min shots you need a high precision of the alignment. I made the PARot program to address this issue: https://sourceforge....projects/parot/

I agree. My Epson scanner I use in "pro" mode, 16 bit tiff output. Pro mode offers manual scan adjustment of the image, 16 bit offers more adjustment of the scanned image. There is still a lot of detail that could be seen in the image that could be brought out. Look at the negative. If you see a dark square then there is too much skyglow is present, decrease exposure time. Check with your lab on the scanning mode. 

 

Joe


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#8 balazs.benei

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Posted 10 September 2021 - 09:34 AM

Thank you all for the replies!

 

The thing is that I've seen much better AP images on Ektar, like Jim's:
https://www.flickr.c...ador/3829654187

My exposure and f stop was almost the same, maybe a better scanning could help. I've asked the lab via email but they didn't answer yet.

 

I have AZ GTi mount which doesn't have polar scope, so I always use Sharpcap, guide scope and ASI 120 MC for polar alignment. I nailed it for the first one but I probably moved it while I set the new target or winded the film... Lesson learned: I should always move the mount via SynScan and wind the film off the mount :)

 

Today I'm gonna make another attempt with the Yashica on Portra 400. 15-20 minutes at f/4 maybe... Wish me luck!



#9 Michal1

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Posted 10 September 2021 - 10:20 AM

Indeed, it could have been the case: if you manipulated the camera or the mount by hand, you could have spoiled the alignment. I should have noticed that the first image is tracked well. Maybe you even kicked the mount without noticing that, given the size of the star trails. Just be more careful.

 

Actually, I realized that my mount gets out off the alignment when I change the lens (EQ6 mount, Pentax 6x7 camera). I have to re-align after changing the lens. But the alignment error that arises from changing the lens is very small. With one hour exposure, stars only become a bit oval.  


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#10 SMigol

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Posted 10 September 2021 - 11:39 AM

The field rotation is a dead giveaway for poor polar alignment.

 

To understand how accurate your alignment must be, you need to eliminate rotation from the guide star to the farthest edge of the imaging field.  In your example, that's going to be at least 5 degrees.  Then figure out the declination for your target - the closer to the pole the more accurate the alignment must be to avoid trailing.  Then you have to ask yourself what is the minimum dimension to ignore star trails (5 arc seconds, 25 arcseconds, etc).  Lastly, you need to know how long your exposure will be.

 

Based on those values, you can run the numbers and determine if you can reach the desired accuracy.

 

Move your exposure, scanning sensitivity, and center your guide star to get best results.

 

I made a google sheet a few years ago that allows you to run those numbers.

 

https://docs.google....dit?usp=sharing

 

Then a colleague helped make it into an android app "Sky Drift Calculator"

 

 

 

 

On the choice of film, I've not been very happy with Ektar.  I prefer Portra 400. 

 

It will respond to airglow to give a green cast.  This will have to be removed in post processing by setting the background value white balance.  Select an area with a known dust cloud as your white balance.  This will help the colors significantly.

 

You can overexpose C41 films.  Try a 1 to 2 stop push as well.

 

For an example of what Portra 400 does:

 

https://www.dropbox.... Portra 001.tif

 

This was shot at 165mm on a Pentax 67 at f4 for 45 minutes with a 1 stop push.  


Edited by SMigol, 10 September 2021 - 11:49 AM.


#11 Michal1

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Posted 11 September 2021 - 06:20 AM

Stephen, do you have any experience with the new E100? How would you compare it with Portra 400 or Ektar 100?



#12 SMigol

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Posted 13 September 2021 - 02:04 PM

I've been playing with the new e100 exclusively for the last two years.

 

It responds very well to the IDAS light pollution filter D1 (not so great with the older P2 filter).  This helps to control the green response from skyglow.  Kodak says to use a CCR10 filter - but I haven't gotten one of those to test.  The curve of that filter attenuates all the green slightly.

 

Really needs a lot of light to make it go.

 

Responds well to a 1 stop push.  2 stop push can be problematic because it compresses the film's already restricted dynamic range.

 

As mentioned above, I prefer the Portra 400 over Ektar 100.  The Kodak datasheet shows slightly better Ha response for Portra 400.

 

In a few weeks I'm going to shoot a large collection of film and may have the time to put some emulsions in for comparison.


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