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Gina's DIY All Sky Camera - Mark 4 - with ZWO ASI185MC


Gina

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I have looked at the possibility of using an astro CCD camera for all sky but there's a problem - the ZWO ASI series of cameras have a back focus of 6.5mm whereas my Atik 460EX back focus is 12.5mm.  It won't focus with a CS lens  :(

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A C-mount lens would have an extra 5mm - still not enough then.

I received the ASI174MM today but it appaently comes without a lens or even a method of attaching one. You can buy an adapter for both EOS lenses and C-mount lenses. That same C-Mount adapter came free with the ASI178MM I bought a month ago so I don't know what they are playing at. Anyway, I used the 178 adapter and discovered a CS lens cannot be positioned close enough on the 174 to reach focus - but C-Mount lens will. I have a good 6mm C-mount lens which I can try, and also with the use of an EOS to C-Mount adapter I had I can try my 10-20mm Sigma zoom lens, finally I also have a C-Mount 2.8-6mm varifocal lens which (if can sort out that auto-iris issue) might also be a good option.

DSC00914_zps3aexzwmi.jpg

ChrisH

 

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I see.  Very strange.  Just checked and nowhere does the FLO info say what the back focus is.  It's specified for some other models.  It must be different from the ASI185 which is 6.5mm (and the ASI1600MM which is also 6.5mm with an extension ring to give 12.5mm for telescopes).  That decides it for me then - I won't be buying an ASI174MM.  I'll need to recheck the other options though.

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I've set up my ASC outside perched on the guttering in the hope there might be some clear sky.  I'm still having problems with USB cables but it's now working with the supplied USB3 cable and without the casing which seems to be spoiling the connection at the camera somehow.  The orientation is with north at the top and east to the right (9 o'clock).  This capture shows the moon just rising above the eastern horizon amongst the clouds.

Capture 2016-07-21 2220.JPG

 

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After that it clouded over completely and I went to bed.

Regarding cameras and lenses, there's something very wrong with the info about ZWO cameras on FLO, I'm sorry to say.  My current ASI185MC definitely has a lower back focus than my Atik 460EX which has a back focus of 12.5mm (confirmed) and yet the info says it's 12.5mm.  I think it's 6.5mm like some other ZWO cameras.  The ASI174MM has no info on back focus and the ASI178MM that I'm thinking of buying is stated as 12.5mm, yet has what appears to be the same 2.5mm f1.2 lens as supplied with the ASI185MC and which I'm using now.

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1 hour ago, Gina said:

After that it clouded over completely and I went to bed.

Regarding cameras and lenses, there's something very wrong with the info about ZWO cameras on FLO, I'm sorry to say.  My current ASI185MC definitely has a lower back focus than my Atik 460EX which has a back focus of 12.5mm (confirmed) and yet the info says it's 12.5mm.  I think it's 6.5mm like some other ZWO cameras.  The ASI174MM has no info on back focus and the ASI178MM that I'm thinking of buying is stated as 12.5mm, yet has what appears to be the same 2.5mm f1.2 lens as supplied with the ASI185MC and which I'm using now.

I don't have a clue what the back-focus requirement of the 174 is, but it's certainly longer than the 178 - and you're right, it did come with a 2.5mm lens.

The difference between a C-Mount and CS-Mount lens in terms of back-focus is 5mm, if you have a camera that supports CS-Mount but want to use C-Mount you have to use a 5mm spacer (like QHY, GPCAM etc...). The fact that when I screwed a C-Mount lens into the adapter (supplied with the 178) screwed into the 174 reached focus, yet a CS-Mount lens would not suggests the back-focus on the 174 is 5mm greater than the 178 (and no doubt your 185). That's not unreasonable though, CS-Mount lenses cannot cover the larger 174-sized sensor and all you would get is a little circular image in the middle of a big black rectangle!

C-Mount lenses generally offer a larger image circle than CS-Mount lenses, and indeed can be used for 4/3 DSLR cameras too. They are also (generally) of higher optical quality/more expensive because of the job they were designed to do. After playing around last night (under cloudy skies) it seems I really need a C-Mount lens somewhere between 2 and 4mm to get full sky cover, the 6mm I tried is a bit too restrictive. I could machine my own threaded adapter which moves the lens 5mm closer to the sensor which no doubt would then allow a CS-Mount lens to work with the 174 but I doubt the results would be great. When I get an idle hour I'll try that out. I have seen a 4mm C-Mount lens offered for sale @ £50 which would be a better option.

ChrisH

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After much searching of the ZWOptical web site I have at last found the dimensions of the camera back focus values.  The 174 is not listed in the main information but I found a PDF manual and the back focus is 17.5mm whereas most of the others are 12.5mm so there is your extra 5mm.  The photos of the various cameras quite clearly show the extra height of the front part of the 174 camera housing.

ASI174 Body cf ASI120 01.JPGASI174 Drawings 01.JPG

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Focus maybe out slightly? I can still recognise the constellations though - and some Milky Way showing through :) It's raining here but there may be some gaps later.

I confirmed earlier that applying 3.3v to pins 3 and 4 (+ and - respectively) fully opens the iris. I have a few circuits to try to get intermediate open settings.

ChrisH

 

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Yes, I may need to adjust the focus a little.

Here's a still capture stretched a bit in PS, resized and saved in PNG.  I'm dying to see how this does when we get a clear night with no moon.  Might just get it dark enough before moonrise in a few days.

Still001.pngStill001a.png

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Regarding focus, I might make a new case big enough to take a small stepper motor and Arduino Nano and turn the lens with 3D printed spur gears.  OR if I can get a Linux capture app working, a Raspberry Pi.

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Chris, did you say you had an ASI178MM plus supplied 2.5mm lens?  If so, what was wrong with that combination for ASC?  I ask because I am thinking of buying an ASI178MM for my ASC.

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40 minutes ago, Gina said:

Chris, did you say you had an ASI178MM plus supplied 2.5mm lens?  If so, what was wrong with that combination for ASC?  I ask because I am thinking of buying an ASI178MM for my ASC.

Yes I have, but the 178 is my Solar/Lunar camera so I've never tried it with the supplied 2.5mm lens. I had to search out the box with the C/CS adapter in it to try on the 174, and that's when I found the lens :)  The supplied lens itself is a bit odd as it screws onto the end of the camera without needing to use the adapter plate (i.e., it has the same diameter thread as the adapter plate itself) so it cannot be attached to any other camera like the QHY or GPCAM which all use a C/CS thread. It will screw onto the 174 of course as it is the same basic camera body but because it's basically a CS lens it cannot reach focus with it. Only a C-mount lens will reach focus on the 174. Complicated isn't it?

If we ever get a clear sky again here I'll take a couple of images using the 178 with the supplied lens.

ChrisH

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