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Mount for film imaging

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#1 Rama777

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Posted 19 July 2020 - 02:57 PM

Hey guys! I’ve been lurking and reading and let me just say that the wealth of knowledge I’ve gained from everyone’s experience is extremely appreciated :))

I recently bought a skywatcher 100ED and I’m in love. I’ve been out all night every chance I can get and it has been extremely rewarding.

I know film has many negatives (no pun intended) compared to digital. I’m not interested in astrophotography to get perfect pictures. I love film, we have a darkroom and the process of getting as good an image I can with film is all I’m after.

I was thinking about a Losmandy or an EQ6, but I have questions, many times be honest but I’ll try to narrow it down to what mount I should get first. I know that periodic error is one of the main things to work towards minimizing. However I also hear that film is only 1/5 as sharp as digital, which I assume means that periodic error and mount steadiness is therefor somewhat less of an issue to getting reasonably sharp images?

So before I go any further, and because money is an issue, I would first like to know if I could get away with a mount that is actually less expensive than the two aforementioned that I’ve been considering?

#2 Rama777

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Posted 19 July 2020 - 03:01 PM

I should perhaps mention that I do intend to auto guide but that process and the necessary equipment that I will need I am still ignorant of for the most part. So I will need a mount one way or the other that will be adequate. As for auto guiding equipment options, I’ll also throw out that I would prefer to not be connected to a computer, and I will be happy to minimize wires to whatever extent I can get away with.

#3 Tapio

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Posted 19 July 2020 - 03:15 PM

Losmandy would be better of the two - and more expensive.

You need autoguiding, especially with film but there are stand alone guiders and best of them is Lacerta MGEN.



#4 Stelios

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Posted 19 July 2020 - 03:27 PM

Moving to film for a better fit/more experience. 

 

This is the F/9 100ED, correct? IMO with such a length you would want the EQ6R-Pro, but you might get away with a HEQ5.

 

Still:

 

"Thank God I saved money on the mount" -- said NO astrophotographer, ever. 


  • Jaimo! and 44maurer like this

#5 Rama777

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Posted 19 July 2020 - 04:15 PM

Cool, cool.. Exactly what issues would I run into with an EQ5 as opposed to the EQ6 or Losmandy?

#6 Rama777

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Posted 19 July 2020 - 04:45 PM

Oh and yes, it is indeed the f/9

#7 OldManSky

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Posted 19 July 2020 - 10:30 PM

"However I also hear that film is only 1/5 as sharp as digital..."

Nonsense.  I don't know where you heard that, but a good fine-grained 35mm film is as sharp if not sharper than most of the digital sensors out there.

The advantage of the digital sensors is that being all-digital, you can take the original and use very good sharpening techniques on it.  While with film, to do that you have to scan it, meaning you're working on a one-generation down copy, which isn't as good as the original, and which won't have all of the dynamic range of the original.  But that doesn't mean film is 1/5 as sharp...that's poppycock :)

 

I have to tell you, though -- I did film astrophotography for a long time.  Because I started doing this before digital was available.  Film is VERY demanding.  Unlike digital, where you can do a large batch of shorter exposures and stack them (throwing out any stinkers along the way), with film it's one long exposure -- and it can be easily ruined.  A little bit of bad guiding, a satellite through the image, kicking the tripod leg...and the worst part is when it happens after you've done a perfect exposure for 2 hours and are just about to close the shutter!  Then there's reciprocity failure -- a sad characteristic of film where it sort of "gets fed up," and loses sensitivity over a long exposure, so that the longer you expose the less it starts collecting photons.  We used to hyper our films ("soak" them in hydrogen gas before heading out -- https://en.wikipedia...ersensitization ) to combat reciprocity failure, with varying degrees of success.  And there are color shifts with certain films over long exposures, and...

Well, like I said, very demanding.

 

I won't try to dissuade you, just warn you:  it ain't gonna be easy.

For a mount, get one with a slow and smooth periodic error that will guide out easily.  Even one with a fairly low PE that's "jerky" and hard to guide would be worse than one with higher PE but a smooth curve that's easily guidable.

 

Good luck.



#8 Rama777

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Posted 19 July 2020 - 11:02 PM

The 1/5 as sharp rumor is something I picked up from these forums actually!

I do understand reciprocity failure and the demands of film, and yeah, those evil satellites are everywhere now and will likely ruin half my attempts, but that’s okay. To be quite honest the more failures I have, the more exciting the successes will be :)

Low LE, jerkiness, or the inverse. These things are all rather mount specific. It does sound like I will need to get one of the ones I mentioned. No chance for me to go any higher. But which mount in the 2,000 dollars or less range has the least amount of jerkiness? Does anyone know the answer to that?

Another question, would a Losmandy sans go-to be workable or is go-to capability all that important for auto-guiding integration?

I was thinking about getting a Losmandy without that option, or the EQ6 which of course comes standard with go-to. The former just looks better engineered but of course looks can be deceiving. The price for the Losmandy is very near the same as the EQ6.

As well, in order to not auto-guide with the aid of a computer, is a stand alone guider where I need to start focusing my research? I like the idea in theory. Though I’m unsure of how that works yet, it sounds like flexure would be less of an issue?

Pros and cons of both methods?

Thank you guys so very much for your input!

Edited by Rama777, 19 July 2020 - 11:14 PM.


#9 TxStars

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Posted 20 July 2020 - 12:52 AM

A Losmandy G11 would be a good choice and allow you to use your current scope and others if (when) you later decide to get more....

Go-To is more for finding objects than anything.. It is not needed, but it is nice to have..

For guiding your refractor an off-axis guider or a guide scope can be used, just make sure either one is properly mounted and adjusted.

Stand alone guiders are good when you don't want to haul a computer into the field. (They have a computer of sorts built into them that takes images of a star and tells the mount how to correct to keep that star centered)

Expect a steep learning curve when you start imaging, as there is a lot of set-up steps you need to follow.

I would recommend starting a camera lens in the 100 - 300 mm range to help get the basics down.



#10 Phil Sherman

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Posted 20 July 2020 - 02:26 PM

While doing film astrophotography is challenging, it's hard to justify it when you can start off with a used/refurbished Canon DSLR for a few hundred dollars or less. Kodak no longer manufacturers the specialty films they used to have for astrophotography and if you want to take images longer than 30 seconds, reciprocity failure is a killer. Hypering film in a hydrogen chamber helps with reciprocity but you'll probably need to build your own. Film needs to be kept in the chamber for hours before use and, if I remember correctly,  the hypering is good for a relatively short interval (hours) after removing the film from the chamber. 

 

Once you have a negative what will you do with it? Print paper is much more limited in dynamic range than negatives and it's impossible to do dodging on individual stars in a negative. Film focusing is also an issue. A viewfinder isn't bright enough for focusing. When I was film imaging with my M3 then M4 Leica, I made a ground glass I could mount in the film plane to focus with a magnifier before inserting the film. Unfortunately, there was no way to compensate for temperature changes in the location of the focal plane without removing the film to refocus. Pulling film out of a cartridge then rewinding it back can also cause defects in the film that will destroy a nice print. My Leica cartridges didn't have that problem because they used a different mechanism to seal the cartridges.

 

The only target I'd recommend for a film camera is the moon. At its brightest, exposures are the same as you would use for daytime landscape photography. One to two additional f/ stops or the equivalent longer exposures is a good place to start for imaging craters along the terminator. Almost any motorized mount with a lunar rate should work for this.



#11 Rama777

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Posted 20 July 2020 - 09:24 PM

I appreciate all the warnings!!

Could you elaborate on why you would need to remove the film for refocusing? Could I not just use the shutter release override every 20 minutes or so to refocus, then reopen it?

Edited by Rama777, 20 July 2020 - 09:25 PM.


#12 TxStars

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Posted 20 July 2020 - 10:50 PM

Depending on the night time temp shifts where you live your refractor or a camera lens may not have too much focus shift.

The key will be to get good focus to start with..

As mentioned a piece of ground glass on the film rails in the camera and a magnifier is the best way.

I use a 60x Takahashi focusing microscope which get me where I need to be.

 

Film imaging is not instant gratification like digital, but for some of us it is enjoyable..

There is nothing wrong with learning how film imaging is done and giving it a try..



#13 Phil Sherman

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Posted 22 July 2020 - 10:21 AM

I appreciate all the warnings!!

Could you elaborate on why you would need to remove the film for refocusing? Could I not just use the shutter release override every 20 minutes or so to refocus, then reopen it?

The Leica I was using is a rangefinder camera. The only way to focus is a ground glass in the film plane. When no film is in the camera, the base plate is removed and the back cover for the film guide rails flips up to give access to the film plane. When I was using this setup, I marked the film when it was loaded so I could reset it to the same spot when reloading the film. I then covered the objective and advanced the film one exposure past the last one I had used after I refocused. I was using bulk loaded Tri-X in the Leica cartridges to prevent scratches on the emulsion from a regular film can's foam seal. The Leica film cartridges are two cylinders with  a slot in both. After the film is inserted in the camera. a fork assembly in the base plate is used to rotate the cylinders to open the slot. The same fork closes the cylinders after rewinding. That fork assembly also locks the base plate to the camera body which prevents opening the camera with the film can open.



#14 Michal1

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Posted 26 July 2020 - 04:39 PM

Let me start with another warning. Personally, I wouldn't do film astrophotography with an f/9 telescope -- too slow. f/6 is my limit. But you can definitely try if you already have the telescope. I would recommend starting with bright targets.

 

Film AP doesn't have to be difficult at the beginning. See here my photos of galaxies taken by an unguided telescope on an unsuitable film and scanned horribly by the nearest lab:

https://www.cloudyni...cope-in-action/

Given that these images took almost no effort, I was very pleased. The better results you demand, the more effort and money you have to spend, of course.

 

Many of us at this forum are using a hybrid workflow when we take the images on film that is scanned after developing and the images are further processed digitally. In this way, you can get rid of the satellite trails and other defects. You can even stack several short-exposure photos like with a digital.  

 

For focusing, I am using a combination of a parfocalized eyepiece and Hartmann mask. This means that I put on the mask and focus in the eyepiece the image of a bright star, then I unscrew the eyepice holder and replace it by the camera. The Hartmann mask it just a cardboard disk with three circular holes. My parfocalized eyepiece is not parfocalized exactly, so I also need a scale attached to the focuser tube. Here are some images focused in this way:

https://www.cloudyni...fujicolor-c200/

I remember that almost no stars were visible on the sky through the clouds when I was shooting the Draco Trio. In spite of this, the photo shows the galaxies much clearer than the eye under ideal conditions :) 

 

I find goto of my mount very useful since it allows me to point the telescope without having to identify the star field in the viewfinder or eyepiece. This makes things much faster.

 

As for the comparison of sharpness of film and CCD, see these images of M101

https://www.astro.cz...C/M101.jpg.html

https://www.astro.cz...ageViewsIndex=1

and M51

https://www.astro.cz...IC/m51.jpg.html

https://www.astro.cz...ageViewsIndex=1

taken through the same telescope. Perhaps some film (Acros 100?) would surpass the CCD, but definitely not every film. I assume that OldManSky speak about the Technical pan film that is no longer in production.




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