Do I really need a more expensive mount?

[Jerry Barnes]

There is a thread in mounts asking for opinions on the EQM35 Pro.  I was interested as I have one and then started thinking about how important a mount is if your equipment is relatively light (like mine).

Do I really need a mount that will give me 20 minute exposures?  The difference in signal to noise ratio between 10 minute subs and 1 minute subs is minimal.  What does make a big difference is light pollution.  If I travel 30 mins to get from bortle 6 to bortle 4 the signal to noise ratio almost doubles.

If I can work with 1 minute subs do I even need to worry much about guiding in Dec?  (The weakness in the EQM35 apparently) The subs will still stack wont they?

I’m thinking I might do better with a light mount that’s portable and spend money on power packs and controlling using a Raspberry Pi rather than a laptop instead of upgrading to an EQ6 Pro say.

Am I missing something here?  Granted I’m limited on the scope I can use.

Signal to noise calculations using https://snrcalc.vercel.app/home Vlav has also produced a spreadsheet to do the calculations.

Heart nebula

Bortle 6, 5 hrs of 1 min subs, snr = 5.8

Bortle 6, 5 hrs of 2 min subs, snr = 5.9

Bortle 6, 5 hrs of 10 min subs, snr = 5.9

Bortle 4, 5 hrs of 1 min subs, snr = 10.9

[Marvin Jenkins]

What a great question. I asked the same thing to a lesser degree having an EQ5. I don’t think there is much of a difference in how I approached AP at my start.

Some others might say no. But I will say you are limited to 60second subs. To go past the minute barrier it would seem you need to guide.

On the other hand there are plenty of examples of images stacked from many sub minute images. I will wholeheartedly agree with you that travelling to really dark dark skies will make a huge difference.

Marv

[ONIKKINEN]

I am on a long and frustrating journey to find every excuse on earth to not have to upgrade my mount (also the EQM-35). I think the answer to do you need one is No, but would you want one? Yes. I hate my mount but i am determined to find the least bad way to use it with my very overloaded setup of 9kg on it, its frustrating and i will definitely upgrade one day, but since then i am trying all kinds of hacks to make it tolerable. So far results are mixed but my setup technically does its job, it just wastes a bit too much precious clear sky for my weather conditions.

 

Not guiding in DEC is a very effective way to tone down the wild seismograph that is the PHD2 log. DEC guiding will affect RA aswell since there will be stiction, backlash, sudden jerks or hiccups that shake the entire mount. Not touching DEC removes a good chunk of these temper tantrums. This relies on good polar alignment and short enough subs to make DEC drift a non issue but polar alignment to this degree is not that hard.

 

I had the idea of taking the mount completely out of the question by taking 5-10s exposures with high gain and live stacking those into 5min subs while capturing. Then just stack and process the resulting "synthetic" 5min subs as you would normally. This would cut down the processing and storage space requirements for the otherwise thousands of subs but still retain the accuracy of a very short exposure. Someone suggested using sharpcap for this as it apparently could livestack a predetermined amount of exposure into a frame, but i actually haven't tried this yet. Why spend fortunes on a mount if software can emulate this? Seems like astrophotography is headed towards software and technology improvements instead of mechanical improvements anyway.

[Lee_P]

2 hours ago, Jerry Barnes said:

Signal to noise calculations using https://snrcalc.vercel.app/home 

That's a potentially very useful site! I just tried it, but found the surface brightness section a bit tricky to fill in. Cartes du Ciel doesn't seem to have the surface brightness for most of the targets I'm interested in. Have you found any workarounds?

Regarding your question, you can get by with short subs with the 2600MC. Guiding is useful though, least of all because it allows you to dither, which is more-or-less essential. So I'd say that if you can reliably get subs of a couple of minutes using your EQM35 with guidescope, then why upgrade? 

Edited November 2, 2021 by Lee_P

[Jerry Barnes]

To get the surface brightness you can use the calculator and provide magnitude and size from stellarium or similar.  Alternatively you can add 8.9 to the surface brightness.  Telescopius has that and probably other sources too.  Easy to make a mistake though.  I'm not familiar with Cartes du Ciel.  

I've not tried to dither yet,  Thats the next thing to try out I think.

 

[malc-c]

Personally, it's not really down to to the precession larger mounts like an HEQ5 / EQ6 /EQ8 offer, although that helps, its their load capacity that becomes a crucial factor.  Adding guidescopes and cameras, and large imaging cameras without impacting the stability of the mount is very important.  

I started with a 200P / EQ5 combo... I became hooked on imaging, mainly as I was disappointed with what I could see visually from my town location.  But the 200P was the limit for the EQ5, and adding even a light weight DSLR it was clear I needed to upgrade the mount.  The HEQ5 carried the 200P, and ST80 with QHY5 guide camera, and a Canon 400D, plus all the cables, and was still stable.  Given the location I run the exposures for no more than 5 minutes at 800 ISO - and with guiding averaging less than an arc second RMS on a good night, I can't complain

[pete_81]

Been there, done it. Only bought one major mount update in (close to) 15 years, but very much needed. I was running a 10", f/4.8 (10kg) OTA for visual on an eq3 equivalent (which came with the scope), and asked myself would the eq5 range (obviously cheaper) would be ok, but advised on SGL that the weight (and possibility of imaging) would realistically require the eq6 range for stability.

It was a tough decision, but worth while investment. I ended up getting the AZEQ6 as it's slightly better for doing visual (AltAz mode with the controller), and would indeed future proof any imaging (with weight of guiding, filters, camera, etc), and the endless list of kit is still building!

I've got into imaging now, and initially used the mount with DSLR and fairly light telephoto lens (500mm mirror) so the mount wasn't taxed in the slightest. I was able to add guiding with this setup and then acquired a smaller, lighter refractor (ST102). Whilst the mount is still OTT for this setup with guiding, I feel it's well future proofed up to anything I'm likely to put on it.

Coming back to the original question, no need to update/upgrade unless your setup is struggling with the weight of kit. If you're tracking decently enough, then no need. If the mount can't handle setup, then thinking about updating may be required, at least in thought! Again, my thoughts, future proofing should be thought about before rushing into it (obviously budget too!). Echoing Malcolm above I believe.

Edited November 4, 2021 by pete_81

[wimvb]

On 02/11/2021 at 20:22, Jerry Barnes said:

Do I really need a mount that will give me 20 minute exposures?  The difference in signal to noise ratio between 10 minute subs and 1 minute subs is minimal.

With a CMOS camera, like the one in your signature, there is no need to take 20 minutes exposures. This is something from the CCD past. For RGB imaging up to 4 - 5 minutes at low gain should be enough, and for NB imaging you simply increase the camera gain and keep the exposures short (5 - 6 minutes). CMOS cameras work best with many, short exposures. So no, in my opinion you don't need a mount that will give you 20 minutes exposures.

[powerlord]

It's a good mount. Keep it unless u need more load. As @wimvb says I've never went longer  than 10 mins (my standard for nb). Anyway if it does 10, it's do 20 surely?  But no point. Plus just longer for Musk's shatalittes to ruin a sub.

Edited November 5, 2021 by powerlord

[Jerry Barnes]

Thanks everybody, you are confirming what I thought.  I'll work on my technique and investigate dithering.  Its not so long till the astronomy show in March so I'll keep the credit card locked up till then at least.