Off-axis guider? Considerations and suggestions?

[SkyHiker]

How the heck people manage to stuff OAG, filter wheel and camera in that about 55 mm?

Here's how I put my rig together, pretty common I think. In the rear is the "Medusa" rig, it helps to have the computer, power and connectivity right there.

I guess the camera is ASI2600 mono?, Which filter wheel, and which OAG?

See my signature. I may have said 31 mm filters earlier, looking at my signature I realized I was wrong, they are 36 mm.

[turboscrew]

Well, I didn't realize that, unlike the ZWO 7x2" filter wheel, the 7x36 mm comes with T2 connections!
The 7x2" comes with M54 connections.

BTW, in case of need, there is a TS-Optics OAG with 9 mm length. May need some adapters, but the adapters may be "zero-length" ones.
https://www.astroshop.eu/off-axis-guide ... th/p,16532

There are not exactly plenty of 36 mm unmounted filters around, but I guess the necessary are available.

[yobbo89]

https://www.firstlightoptics.com/starli ... wheel.html

have you checked out starlight express fw ?

it's 41.6mm with the adapters for your gear. it gives you 13.4mm to space out the camera using a 55mm back focus cc, you will not filt in a tilt ring and you can't attach cameras that have a built in tilt ring like the zwo asi range ie asi2400 ,asi071,asi6200 these are 17.5mm back focus cameras while the earlier modles are 6.5mm ...

[yobbo89]

dosn't tom have one of these ? 91.5mm back focus

https://www.highpointscientific.com/baa ... ocus-rcc-i

[yobbo89]

There are not exactly plenty of 36 mm unmounted filters around, but I guess the necessary are available.

maybe the 8 pos zwo filterwheel will do ? the filters sit close to 10mm from most camera chips , should be plenty for unmounted 31mm filters on a aps-c, overal the fw is 20mm thick with both ends female t-thread (42mm x 0.75mm)
https://www.highpointscientific.com/zwo ... efw-8x1-25

[turboscrew]

There are not exactly plenty of 36 mm unmounted filters around, but I guess the necessary are available.

maybe the 8 pos zwo filterwheel will do ? the filters sit close to 10mm from most camera chips , should be plenty for unmounted 31mm filters on a aps-c, overal the fw is 20mm thick with both ends female t-thread (42mm x 0.75mm)
https://www.highpointscientific.com/zwo ... efw-8x1-25

Hmm, I checked in astroshop.eu and teleskop-express.de, and it looks like all in all there's about equal number of 31 mm and 36 mm. Astroshop had actually only few of them: 9 items of 36 mm and 6 items of 31 mm.
A lot more of both in teleskop-express, but hard to search.
Got to have another look at that.

I'd rather not order outside Europe, because I've had some bad experience about the customs.
About 230 eur thing, when ordered from England last year, came to cost me 444 eur.

[SkyHiker]

There are not exactly plenty of 36 mm unmounted filters around, but I guess the necessary are available.

maybe the 8 pos zwo filterwheel will do ? the filters sit close to 10mm from most camera chips , should be plenty for unmounted 31mm filters on a aps-c, overal the fw is 20mm thick with both ends female t-thread (42mm x 0.75mm)
https://www.highpointscientific.com/zwo ... efw-8x1-25

Hmm, I checked in astroshop.eu and teleskop-express.de, and it looks like all in all there's about equal number of 31 mm and 36 mm. Astroshop had actually only few of them: 9 items of 36 mm and 6 items of 31 mm.
A lot more of both in teleskop-express, but hard to search.
Got to have another look at that.

I'd rather not order outside Europe, because I've had some bad experience about the customs.
About 230 eur thing, when ordered from England last year, came to cost me 444 eur.

I would be careful about the 31 mm because I almost have vignetting issues with my 36 mm (though it may be mostly because of the CC). When I checked out the ASI2600 equipment this came more or less as a set, they specify that 36 mm is appropriate for the ASI2600 (an APS-C sized sensor). That suggests to me that ZWO thinks that 31 mm is too small. I don't believe ZWO asks more of their customers than they should spend.

[turboscrew]

maybe the 8 pos zwo filterwheel will do ? the filters sit close to 10mm from most camera chips , should be plenty for unmounted 31mm filters on a aps-c, overal the fw is 20mm thick with both ends female t-thread (42mm x 0.75mm)
https://www.highpointscientific.com/zwo ... efw-8x1-25

Hmm, I checked in astroshop.eu and teleskop-express.de, and it looks like all in all there's about equal number of 31 mm and 36 mm. Astroshop had actually only few of them: 9 items of 36 mm and 6 items of 31 mm.
A lot more of both in teleskop-express, but hard to search.
Got to have another look at that.

I'd rather not order outside Europe, because I've had some bad experience about the customs.
About 230 eur thing, when ordered from England last year, came to cost me 444 eur.

I would be careful about the 31 mm because I almost have vignetting issues with my 36 mm (though it may be mostly because of the CC). When I checked out the ASI2600 equipment this came more or less as a set, they specify that 36 mm is appropriate for the ASI2600 (an APS-C sized sensor). That suggests to me that ZWO thinks that 31 mm is too small. I don't believe ZWO asks more of their customers than they should spend.

To me it might work. Due to the tube size, I cant use full-size sensor anyway. I'm searching something with diagonal closer to 20 mm. I remember the discussion with @OzEclipse .

[SkyHiker]

To me it might work. Due to the tube size, I cant use full-size sensor anyway. I'm searching something with diagonal closer to 20 mm. I remember the discussion with @OzEclipse .

Do you have a link? Rob is going for full size and he knows what he is doing, he you and I have the same 12" F/4 so is it not a matter of replacing the focuser?

You will be spending a good deal of money so the scope will be a cheap attribute relatively speaking. My 12" Newt was about $0.8K for instance, the ASI2600MM + FW + electronic focuser + filters were $3.8K including taxes, the OAG + autoguider about $0.4K, the Medusa about $0.2K so $4.4K altogether. The FW + filters were about $1K, I doubt if you save a whole lot of money by choosing 31 mm. (7 filters is right, I don't know why there are 8 filter wheels). For me the APS-C ZWO offering was a breakthrough in value, I got into the market at just the right time.

You will need to add a scope or two with a wider FOV anyway because your FOV will be quite narrow with what you propose, how will you image M31, M42, M45? They don't fit. Panoramas are a major PITA. For most popular DSOs you can get by with a much cheaper setup such as my AVX with a Redcat51 or ED80 or MN152 (the latter is actually heavy enough that the G11S is better).

[turboscrew]

To me it might work. Due to the tube size, I cant use full-size sensor anyway. I'm searching something with diagonal closer to 20 mm. I remember the discussion with @OzEclipse .

Do you have a link? Rob is going for full size and he knows what he is doing, he you and I have the same 12" F/4 so is it not a matter of replacing the focuser?

You will be spending a good deal of money so the scope will be a cheap attribute relatively speaking. My 12" Newt was about $0.8K for instance, the ASI2600MM + FW + electronic focuser + filters were $3.8K including taxes, the OAG + autoguider about $0.4K, the Medusa about $0.2K so $4.4K altogether. The FW + filters were about $1K, I doubt if you save a whole lot of money by choosing 31 mm. (7 filters is right, I don't know why there are 8 filter wheels). For me the APS-C ZWO offering was a breakthrough in value, I got into the market at just the right time.

You will need to add a scope or two with a wider FOV anyway because your FOV will be quite narrow with what you propose, how will you image M31, M42, M45? They don't fit. Panoramas are a major PITA. For most popular DSOs you can get by with a much cheaper setup such as my AVX with a Redcat51 or ED80 or MN152 (the latter is actually heavy enough that the G11S is better).

The discussion:
viewtopic.php?f=4&t=19394&start=60#p163222
The main problem is, that the tube is too small - not enough room between the mirror and tube wall.
That, mainly, causes the vignetting.

About the filters, who knows what weird ideas I might get. BTW, there are 9 slot wheels too...
The time shows what I'll end up with.
I already have a planetary camera, Omegon veLOX 178C. It's not listed in my equipment, because I haven't got a chance to try it out yet. That's small (and cheap).

[turboscrew]

Hmm, this might be the thing you wanted to see.
viewtopic.php?f=4&t=19394&start=40#p163207

[SkyHiker]

The discussion:
viewtopic.php?f=4&t=19394&start=60#p163222
The main problem is, that the tube is too small - not enough room between the mirror and tube wall.
That, mainly, causes the vignetting.

About the filters, who knows what weird ideas I might get. BTW, there are 9 slot wheels too...
The time shows what I'll end up with.
I already have a planetary camera, Omegon veLOX 178C. It's not listed in my equipment, because I haven't got a chance to try it out yet. That's small (and cheap).

I ran the Newt web calculator for my GSO 12" F/4 astrograph and get 75% illumination at a 41.6 mm diameter. It has a 3.25" focuser tube and a mirror minimum diameter of about 81 mm (I had to measure this inside the scope, the long axis seemed about 4.5"). So I'm fine.

Your scope has a 75 mm secondary and 0.5" clearing around the primary so the numbers will be less, I don't have all the info here. Note that 75% illumination is not horrible, the standard deviation is the square root of the mean for Poisson distributions and sqrt(0.75) is not that far from 1 - so flats can easily correct that, also the focus is usually on the center and the stars at the edges are decoration.

Considering what you have invested in your mount and that imager that you have in mind, if your Newt is a problem w.r.t. the desired image size you may consider replacing it with an astrograph - because it is about the cheapest component of everything you have (well, looking at US prices for something like mine). Getting a moonlite focuser will cost more and will solve only half the problem. Or just live with it and realize that your OTA is a compromise for an astrograph, and get the smaller and cheaper parts that you have in mind.

But if you stick with it your FOV will be relatively small and you need to add some more scopes that have a wider FOV. If want towards a full frame like what Rob has in mind your FOV will be larger but it will still not be good for the popular large DSOs, and everything is much pricier. So, nothing wrong with your plan just expect at some point you will want more scopes.

[turboscrew]

I'm keeping that in mind. I'm not sure how far I'll go in to the AP world. And in what sense.
(Yes, I'm a bit weird.)

[turboscrew]

Nice! Looks lime my options just broadened.
I talked with some fellow Finnish astronomers on the URSA forum, and they said that the temperature restrictions needn't to be taken too seriously. One of them mentioned having 2 nights session with ASI071MC Pro in -15°C without any problems. (The cam has specified operating temperature range -5°C to +45°C).

So I guess, most cameras are back in!

[JayTee]

This brings up an interesting notion. Most of the advanced cameras come equipped with a cooler, and if I'm not mistaken it is a thermoelectric cooler, TEC. Also if I'm not mistaken these coolers can also be used as heaters although I've never tried to heat my sensor, I wonder if it's possible to do that just by setting the temperature from your ambient -15 to - 20 to a camera sensor temperature of -5. Hmmmmm.

[turboscrew]

This brings up an interesting notion. Most of the advanced cameras come equipped with a cooler, and if I'm not mistaken it is a thermoelectric cooler, TEC. Also if I'm not mistaken these coolers can also be used as heaters although I've never tried to heat my sensor, I wonder if it's possible to do that just by setting the temperature from your ambient -15 to - 20 to a camera sensor temperature of -5. Hmmmmm.

Yes. They usually use Peltier elements. Making it heat instead of cool requires reversing the voltage.
If it's controlled by DAC + power amp, the polarity can't usually be reversed. Technically very possible, though.
And I think in some cameras that is done - at least "partially" by making the "zero" of the element a bit higher than the zero of the amp. That's used for dew protection.

The sensor chips usually can handle temperatures below -20°C. It's the rest of the electronics I'm worried about.
Like electrolyte capacitors. Or the crystal frequency.

Typically the datasheets of image sensors are very hard to find, but this is one (OnSemi MT9J003).
https://www.onsemi.com/pdf/datasheet/mt9j003-d.pdf

Operating Temperature −30°C to +70°C (at Junction)

[yobbo89]

This brings up an interesting notion. Most of the advanced cameras come equipped with a cooler, and if I'm not mistaken it is a thermoelectric cooler, TEC. Also if I'm not mistaken these coolers can also be used as heaters although I've never tried to heat my sensor, I wonder if it's possible to do that just by setting the temperature from your ambient -15 to - 20 to a camera sensor temperature of -5. Hmmmmm.

Yes. They usually use Peltier elements. Making it heat instead of cool requires reversing the voltage.
If it's controlled by DAC + power amp, the polarity can't usually be reversed. Technically very possible, though.
And I think in some cameras that is done - at least "partially" by making the "zero" of the element a bit higher than the zero of the amp. That's used for dew protection.

The sensor chips usually can handle temperatures below -20°C. It's the rest of the electronics I'm worried about.
Like electrolyte capacitors. Or the crystal frequency.

Typically the datasheets of image sensors are very hard to find, but this is one (OnSemi MT9J003).
https://www.onsemi.com/pdf/datasheet/mt9j003-d.pdf

Operating Temperature −30°C to +70°C (at Junction)

i would assume the rest of electronics would be safe, most electrolytic caps are rated for -40c to +85c , ceramic multilayer smd caps can be around -55c to +175c ,standard radial crystal -40 c to +85c ectt, it seems almost all off the shelf electronic components fall into this spec , i would be more concerned with any ic chips whether the manufacture used higher quality revision for better temp rang and moister as usualy only the camera cmos/ccd chip is the only part sealed ...

if i were using an astronomy camera in a sub deg country i would be wraping a heater strip around the back end of the camera and letting the cameras peltier balance out the temp , peltiers don't work well if the heater end is cold .

[turboscrew]

I'm thinking of 2 cameras now.
Omegon Camera veTEC 16000 M Mono
https://www.astroshop.eu/astronomical-c ... no/p,63068
and
ZWO ASI 294 MM Pro Mono
https://www.astroshop.eu/astronomical-c ... no/p,68797

ASI is winning, but I wonder if it's up to the weathers here.
I sent an e-mail to ZWO about that, but they'll probably respond sometime next week.
I _think_ both of those fit...

[turboscrew]

Hint to @SkyHiker too...

You can, probably, save some millimeters by using these:

9 mm OAG
https://www.teleskop-express.de/shop/pr ... -9-mm.html

Zero-length adapter OAG/T2
https://www.teleskop-express.de/shop/pr ... OAG16.html

Zero length adapter T2/OAG
https://www.teleskop-express.de/shop/pr ... short.html

[SkyHiker]

Hint to @SkyHiker too...

You can, probably, save some millimeters by using these:

9 mm OAG
https://www.teleskop-express.de/shop/pr ... -9-mm.html

Zero-length adapter OAG/T2
https://www.teleskop-express.de/shop/pr ... OAG16.html

Zero length adapter T2/OAG
https://www.teleskop-express.de/shop/pr ... short.html

Thanks, it may help but so long as my stars are round I won't worry too much about it. BTW I have two 48x42 mm adapters (your last link), IIRC they come with the ASI2600s that I have. And one of them is inside my MM configuration. The other one may be in the MC, I need to check.