15 replies to this topic

[Isaac M.]

Hello everyone, I am getting a summer job in which I will make 2000 usd. I am considering using that money on a new telescope. I currently have an AM5 and wo gt81IV. I Would like to not get a new mount and still use the AM5, however I would consider selling the GT81. Let's say I have a 2,700 usd budget if I sell. I am still in high school so my parents are not dying to store a c14 in the garage, so I would be looking for something portable to an extent. I have loved the 81, so a refractor would be great. I want something with quite a bit more focal length than the GT81 though. I would love to keep both, but if there is a much better option and it's better to sell then I'm willing. I am really open to any options just keep rolling them out! I will also buy used so starting price can be over as long as I would be able to find it at my budget used, I'm willing to be patient and wait a bit for a good deal to come up.

 

Thanks in advance,

 Isaac Metcalf

[AstroFrankMontana]

What do you wish to image that the GT81V is the limiting factor?

 

For a longer focal length, and using the same mount you already have, The Celestron Edge 9.25" SCT will give you a 2000mm focal length and about 400-600USD extra to spend on the guide scope and camera. The Telescope is under 7KG, well within an AM5's weight limit.  And now you have TWO setups. One for wide field, one for up close.  Both telescopes are small enough to be stored in a bedroom and drive to remote sites for darker skies when possible.

 

Always start your decision with "What problem am I trying to solve?"  Something to think about.

[auroraTDunn]

It really depends on what you desire to image the most, nebula (non-planetary) and other widefield objects or galaxies, globs, planetary nebula's. If the former then make sure you stay with a fast scope, obviously if you want the later then a larger aperture and longer focal length. Either way I would try and stay with a refactor and if possible a petzval design, it makes life so easy and glorious!!! Another possibility which will be right at your upper limit in a few ways would be to go with a 8" RASA, I have seen them on an AM5 but you will want to get counter weights. I have seen MANY great images of pretty much any object with an 8" RASA but I have never used one myself.

[Isaac M.]

What do you wish to image that the GT81V is the limiting factor?

 

For a longer focal length, and using the same mount you already have, The Celestron Edge 9.25" SCT will give you a 2000mm focal length and about 400-600USD extra to spend on the guide scope and camera. The Telescope is under 7KG, well within an AM5's weight limit.  And now you have TWO setups. One for wide field, one for up close.  Both telescopes are small enough to be stored in a bedroom and drive to remote sites for darker skies when possible.

 

Always start your decision with "What problem am I trying to solve?"  Something to think about.

The problem I would be trying to solve is that right now I don't really have anything to image. i only have a good view of the north sky so I can't shoot big galaxies like andromeda and bodes. There aren't many nebulae to my knowledge up right now so I have been waiting a month or so and probably have a bit more time to wait. So maybe the answer is just don't image right now and save the money and be patient. I am interested in imaging galaxies and nebulae.

[dcm_guitar]

I'm assuming you're relatively new to the hobby.  Sounds you like you may have contracted a case of focal length fever.  I've had it.  It's expensive.  If you want a lot more focal length factor in the cost of an OAG and OAG camera.

My short answer is you should keep the GT81IV.  It's an absolutely fantastic OTA and is a wonderful astrograph.

 

This topic and question comes up annually and there is a LOT of interesting and educational reading on here.  The insanely short version is:

First, what's your camera?  You need to know the specs.  I'm going to assume it's something like a ZWO 2600 with 3.76µ pixels.

What's your image scale?  With a GT81IV and a camera with 3.76µ pixels your image scale is ~1.6"/px.  

 

A good rule of thumb for imaging is that you want to sample at ~3x your seeing.  If your seeing is 2 seconds, your sampling should be ~0.67"/px.  If your seeing is 1.5" then your sampling is 0.5"/px.

 

If your camera has 3.76µ pixels and your seeing is generally around 2" then your focal length should be ~1,150mm.  If your seeing is 1.5" then your focal length should be ~1,500mm.

Obviously, you can bin your pixels and the new AI based algorithms do an amazing job of clarifying detail in your images.  

 

After a LOT of research you're going to fund that a nice refractor astrograph with that focal length is a LOT of money and perhaps beyond the capacity of your AM5.

 

A reflector will get you the focal length you want but many are kind of slow.  Then you start asking for the best 1,200mm f/5 reflector.

 

[Isaac M.]

The problem I would be trying to solve is that right now I don't really have anything to image. i only have a good view of the north sky so I can't shoot big galaxies like andromeda and bodes. There aren't many nebulae to my knowledge up right now so I have been waiting a month or so and probably have a bit more time to wait. So maybe the answer is just don't image right now and save the money and be patient. I am interested in imaging galaxies and nebulae.

Sorry I meant to say i only have a good view of the south

[dcm_guitar]

The problem I would be trying to solve is that right now I don't really have anything to image. i only have a good view of the north sky so I can't shoot big galaxies like andromeda and bodes. There aren't many nebulae to my knowledge up right now so I have been waiting a month or so and probably have a bit more time to wait. So maybe the answer is just don't image right now and save the money and be patient. I am interested in imaging galaxies and nebulae.

The other thing I'd say is that a galaxy imaging rig and a nebulae imaging rig are somewhat different.  You've got the start of a great rig for nebulae imaging, but you've also found that this time of year is tough due to lack of good targets.  Do you have narrowband filters?  The Sadr region is coming up and it has LOTS of fun things to capture.

This hobby demands patience.  I'd simply say be patient and wait for the targets to come around.  They do every year.  I know it's tough now, but from October to February your rig is kind of ideal.

It's also fun to learn and try to plan your "ideal" galaxy rig.  For me, I have to make it portable because I need to travel to darker locations.  That means 10" is my absolute maximum aperture and 8" is a bit more realistic.  Because I need to travel to dark sites I want to make my data capture as efficient as possible, so I emphasize faster focal ratios.

Start looking at different telescopes and configurations.  Identify your preferred setup.  Ask questions.   Cruise the classifieds area here.  Spend time looking for images on astrobin with the setup you're considering.  The time will go by quickly.  It will also freak yu out at how expensive the system you want is.

[Notdarkenough]

If you want to image galaxies, you certainly need focal length, as you posted. What kind of Seeing do you have? Maybe an 8" EdgeHD would be better than a 9¼. There are many threads about EdgeHD vs Standard, but I find the 1 obvious difference is at f/10. If you want to image at f10, the EdgeHD will not need a flattener, and will work well. If you always want to reduce the focal length to around 1400mm, maybe a standard C8 and a Starizona SCT flattener/reducer is for you.

[Isaac M.]

I'm assuming you're relatively new to the hobby.  Sounds you like you may have contracted a case of focal length fever.  I've had it.  It's expensive.  If you want a lot more focal length factor in the cost of an OAG and OAG camera.

My short answer is you should keep the GT81IV.  It's an absolutely fantastic OTA and is a wonderful astrograph.

 

This topic and question comes up annually and there is a LOT of interesting and educational reading on here.  The insanely short version is:

First, what's your camera?  You need to know the specs.  I'm going to assume it's something like a ZWO 2600 with 3.76µ pixels.

What's your image scale?  With a GT81IV and a camera with 3.76µ pixels your image scale is ~1.6"/px.  

 

A good rule of thumb for imaging is that you want to sample at ~3x your seeing.  If your seeing is 2 seconds, your sampling should be ~0.67"/px.  If your seeing is 1.5" then your sampling is 0.5"/px.

 

If your camera has 3.76µ pixels and your seeing is generally around 2" then your focal length should be ~1,150mm.  If your seeing is 1.5" then your focal length should be ~1,500mm.

Obviously, you can bin your pixels and the new AI based algorithms do an amazing job of clarifying detail in your images.  

 

After a LOT of research you're going to fund that a nice refractor astrograph with that focal length is a LOT of money and perhaps beyond the capacity of your AM5.

 

A reflector will get you the focal length you want but many are kind of slow.  Then you start asking for the best 1,200mm f/5 reflector.

 

Thank you for the detailed response, I have the asi 183mm pro and astrodon 5nm SHO 1.25inch and zwo lrgb 1.25. So would it be better to get a 2600mm or something like? I would also need to get new bigger filters and filter wheel though, right?

Edited by Isaac M., 11 May 2025 - 07:40 PM.

[Isaac M.]

If you want to image galaxies, you certainly need focal length, as you posted. What kind of Seeing do you have? Maybe an 8" EdgeHD would be better than a 9¼. There are many threads about EdgeHD vs Standard, but I find the 1 obvious difference is at f/10. If you want to image at f10, the EdgeHD will not need a flattener, and will work well. If you always want to reduce the focal length to around 1400mm, maybe a standard C8 and a Starizona SCT flattener/reducer is for you.

I am honestly not sure what seeing I have, I live in Kansas City B8

[Isaac M.]

  I'd simply say be patient and wait for the targets to come around.  

That is probably what I will end up doing, and maybe look into a different camera.

[dcm_guitar]

Thank you for the detailed response, I have the asi 183mm pro and astrodon 5nm SHO 1.25inch and zwo lrgb 1.25. So would it be better to get a 2600mm or something like? I would also need to get new bigger filters and filter wheel though, right?

I looked up the 183mm specs and it has 2.4µ pixels.  That's pretty darn small.

A good rule of thumb is you probably average around 2" seeing.  On good nights it may get down to 1.5" on bad nights it's probably 2.5".  For the purposes of matching your sampling to your seeing with the camera you own, a 2" seeing estimate is likely accurate enough.

The math says with 2.4µ pixels, 2" seeing and 3x sampling you likely max out at ~740mm of focal length.  On good nights it's probably ~990mm.  With your current camera you're really not buying yourself any additional detail with anything over ~1,000mm of focal length.

The GT81IV is a really nice astrograph.  Do you have the flattener for it?  If not, that's probably the best place to spend your upgrade budget.  After obtaining the flattener I'd look into upgrading your camera.  That can be an expensive upgrade.  Something with an IMX571 sensor is a great place to look.  I think your 1.25" filters will work with APS-C.  The little ZWO auto focusers work reasonably well without breaking the bank.  

I'd look into a flattener, a camera, an autofocuser and a really robust automation solution for capturing data (e.g. NINA and a miniPC) before chasing down more focal length.

 

[jml79]

I have a lot of experience with small pixel imaging (your 183 is a small pixel camera). The GT81 is a really nice scope and pairs with the 183 nicely. It really is a never sell scope. If you don't have both the Flat GT 1.0 and the Flat 6AIII 0.8x then I would buy those. Then I would actually consider buying an inexpensive, very wide scope like an Askar FMA180. I know it's not a galaxy rig but you would be surprised what wide field imaging can be like.

 

A budget galaxy rig would be a used 8" SCT always with a reducer (Starizona SCT reducer) and an IMX 533 camera. Any IMX533 is fine but the SVBony SV605CC is very inexpensive. This rig would get you into some pretty tiny sampling and be a huge learning curve. It would also benefit from an OAG-L and an ASI220 guide camera as a minimum. A lot of stuff to buy and might be best to wait another year. A reduced C8 with a 533 camera gets you into some tight but doable sampling around 0.6 arcseconds. It will push all of your skills.

[Sacred Heart]

Hello everyone, I am getting a summer job in which I will make 2000 usd. I am considering using that money on a new telescope. I currently have an AM5 and wo gt81IV. I Would like to not get a new mount and still use the AM5, however I would consider selling the GT81. Let's say I have a 2,700 usd budget if I sell. I am still in high school so my parents are not dying to store a c14 in the garage, so I would be looking for something portable to an extent. I have loved the 81, so a refractor would be great. I want something with quite a bit more focal length than the GT81 though. I would love to keep both, but if there is a much better option and it's better to sell then I'm willing. I am really open to any options just keep rolling them out! I will also buy used so starting price can be over as long as I would be able to find it at my budget used, I'm willing to be patient and wait a bit for a good deal to come up.

 

Thanks in advance,

 Isaac Metcalf

Issac,

 

You have a great system right now.  Take the advice given above and be patient.  In your patience research different scopes and cameras, take note of what they can do, FOV and cost. 

 

Astronomy Tools will show you approximate FOV of just about any camera and scope out there, of almost any target.

 

https://astronomy.to.../field_of_view/

 

Your mount is a good one, do not sell it short.  It should do a C8 maybe that C9.25, yes the counter weight shaft and counter weight will be needed, that's easy and okay.  That can handle a 130mm / 910mm refractor with the counter weight installed.  Pier extensions also, maybe two of them stacked.

 

When you jump up to a larger scope, more weight and focal length, secure the tripod - weigh it down or tie it down to the ground.  Do not want it to spill over.  Also, stability is king when it comes to long focal lengths.

 

To better understand astro imaging get this book,

 

https://www.amazon.c...d/dp/0999470949

 

it explains a lot. 

 

Astronomy, not just imaging, is about your mount and tripod.  Weight, focal length, physical size  all affect tracking and pointing.  Weight is just heavy, physical size - take into account a barbell and a dumbbell, both 20 pounds, a dumbbell is an easy one hand grab with good control, a barbell - same weight becomes a two hand grab because of it's length. Also, physical size could increase your wind resistance.  Focal length, this goes to image scale, your tracking / guiding error needs to be less than your image scale.  All mount related.

 

You have a capable mount, work with it, be patient, research.  Don't let those images fool you,  these people are magicians when it comes to imaging.  They are very good at what they do.

 

Take this time to get that book,  look into your dream telescope, see and realize what it is going to take to do what you want to do.  Hobbies are very expensive AND unforgiving, astronomy is NO exception.  Know what you want AND why you want it.

 

Focus now on you fundamentals, PA, pointing / guiding, imaging and processing.  Maybe slip an eyepiece or two in and take a look.   Lots to offer here.

 

Joe

[Isaac M.]

Thanks everyone for all the advise so far! I do have the WO 0.8 reducer and the auto focuser. So the camera would be the upgrade if any, some have said it will work with my 1.25 filters, I would just want to be sure of that though. I have Astrodon 5nm sho filters so I don’t really want to get different filters. It would probably cost too much to get the asi 2600 and new astrodon filters, so if the 1.25 work I will probably get the 2600 at some point.

[erictheastrojunkie]

I would recommend getting....nothing, right now. By the time you decide on a scope, buy, get it, get it up and running well with all the kinks ironed out....galaxy season will be at its end. If you go with any of the options for galaxy season you are going to need a reflector, even just a wider Newt like my 8" f4. Those options all require a bit more (or A LOT) more work than a refractor in terms of getting good results and that work takes time to learn and implement. You can already image several nebula later in the night, the entire Cygnus and milky way core region rises above 30 degrees after 1am local time, I've already completed an h-alpha portion of the Cygnus Wall image I'm wanting to complete this year in the last couple weeks. At this point you should be planning and starting projects you want to complete in the next 3 months and most of those are going to be nebula/non-galaxy targets. Unless you can only image to the west, galaxy season is pretty much at its midpoint or beyond and nebula "season" is getting going.