Jerry Barnes

I shall go to the Practical Astronomy Show in a couple of weeks and may accidently have to buy some new gear (!). Could I make sensible use of a 1000mm focal length scope on my mount? Alternatively do you get good results from something like a Skywatcher 200 PDS on something like a EQ6R? Or to put the question a different way if I know the guiding error in arc seconds and the arc seconds per pixel of my scope and camera what ratio can I push it to? My camera has a pixel size of 3.8 and astronomy tools calculates 0.78” per pixel at 1000mm focal length which it considers ok for average seeing. If the guiding error was also 0.78”RMS does that affect the answer? I’ve found some reference to similar questions elsewhere that would merit some proper study but will take some time to get my head round properly.

Last summer I had been thinking about mount performance and wondered if a Dark Frame tune would be a good investment. I saw on their website that you needed to book a two week slot for the work. That was encouraging as it implied that they had done something about the complaints of extended delays in returning mounts after working on them. I enquired about availability in the summer when being without a mount would not be an issue. I received a call from Dark Frame in a couple of days and was told a slot had just come free and if I got the mount to them early the next week they would start work on it. I was also told I could probably expect sub second guiding after the work was done. The sales pitch was convincing and I paid in advance as required and despatched the mount in packaging supplied by Dark Frame. Over the next 10 weeks I requested an update on progress several times and if I got a reply it was generally the work would be completed soon. After taking legal advice I wrote saying I expected work to be completed and the mount despatched within 7 days or I would be seeking a cost reduction. I got an apology almost immediately and the mount was despatched the next day. It was a week or two before I had the opportunity to try the mount and see how it performed. I achieved between 2” and 4” RMS generally. I emailed Dark Frame attaching the guide logs and got a very prompt and helpful reply. Essentially the guiding corrections were too aggressive and over correcting given the improved performance following a tune. I reset and redid the PHD2 calibration after setting the corrections for guide pulse width in EQMOD at or below recommended values. After that I could get guiding error to 1.2” at best but nearer 2” or more usually. I was still seeing random spikes, especially in Dec, where there would be a large error, 10s or arc seconds, taking some time to correct. I had noticed that it improved after a meridian flip and eventually realised that the balance was poor and by happy accident was running east heavy. My balance was out because the RA axis was quite stiff and the counter weight needed moving two or three inches to make a difference in the balance. Essentially the mount performance had improved but not as much as I had hoped. Dark Frame give a two year guarantee on their work so I could have continued trying to improve the performance but I decided that it wasn’t worth pursuing and I’d cut my losses and replace the mount.

I’ve had a GEM45 for a few weeks now and its had a few outings. Generally I’m pleased with the mount but only just getting to know how to use it. It looks well made and is nicely finished which is good as it wasn’t cheap. If the legs aren’t extended then its footprint is a bit smaller than my EQM35. It still feels perfectly stable though. I haven’t tried to use the internal wiring to connect USB and power to the head as I think I need more power and USB3 not 2. However I will have another look at that at some point, for now I’m keeping my cable in the same configuration I had before. With the clutches dis-engaged the RA and Dec both move very freely, no friction I can detect. In fact getting balance is tricky as its very sensitive. As I have a focuser fitted the scope centre of gravity is off centre and in Dec it has a tendency to rotate till the scope is horizontal and the focuser at the bottom. Its also very dependant on how much the cable weight is supported or not. When first connected the mount seemed very picky about my USB setup. A single USB connection links both the mount and the iPolar camera. With that connected directly to my PC I could use iPolar but add in a hub or an extension lead and iPolar refused to connect. That’s ok though as when I’m polar aligning I need to be beside the mount. After that the mount connects to a 4 port hub and then via an extension lead to my docking station thingy (using a Surface Book). The iOptron iPolar software is very easy to used and much easier than the polar scope, as it should be. Fairly similar to Sharpcap which I used to use but doesn’t need the RA rotation as part of the process. Sharpcap is there as a backup if I need it and is perhaps more responsive. I don’t know which is more accurate, probably both are good for purpose. Mechanically the adjustment of the mount to get the alignment is much smoother which helps a lot. PHD2 is reporting better alignment than previously as well. iOptron mount control isn’t as sophisticated as EQMOD but didn’t give any problems at first. I’ve later had problems with meridian flip and initial investigation suggests its user error and not setting it up properly. By default after the meridian is reached the mount stops tracking and throws an error if you ask it to flip (I think). Either that or the pre-flip plate solve fails as the starts trail. The advice seems to be set the mount to stop 5 mins after meridian and the controlling software to flip 2 mins after meridian. Something like that anyway, next clear night will be a chance to check that all out. I did get one occasion where plate solving just wouldn’t work and when eventually went outside to check the scope was pointing downwards not at the sky! Again almost certainly my fault, possibly not setting the zero position before starting. I think that was the time when I had to do the classic turn off and on (mount and PC) to get it all synched again. Turning off just the mount or just the PC didn’t seem to work. I’ve not tried to set up PEC but the documentation suggests its easy to do. Given the clutches have to be disengaged before moving the axis manually I think once setup PEC will stay and the worm positions wont change unlike with EQMOD but I could have got that completely wrong. Now to the important bit, does it track well? Its certainly better than my old mount but it really ought to be. There aren’t the random spikes I used to get. I’m getting guiding error varying between 0.6” RMS and 1.3” RMS. Monday night it was between .7” and .8”all night. It seems to be target dependendent and likes to be a little east heavy. I’m not convinced about that yet but need some more investigation and confirmation. I’d prefer not to have to mess with the balance halfway through a session but if that’s what it takes… More investigation and calibration to do. All in all I’m reasonably happy with it, if I can reliably get guiding error to 1” or less I will be. One of the reasons I chose the mount rather than the obvious EQ6R was the weight. I can carry the GEM45 but would struggle with the EQ6R and at some point would like to take it away from the city and get to bortle 4 instead of 6.

Just arrived from FLO. Now I can put my scope on my new mount without catching the focuser.

I've just bought a Losmandy-Style Dovetail Bar from FLO just the same reason. With the original dovetail on my Z61 it sits too low in the saddle and the focuser makes it really hard to get the right balance. The Losmandy sits higher. FLO very helpfully gave me a couple of options, the Losmandy will let me fist a safety stop on the dovetail which should prevent a nasty accident if the saddle isn't tight enough.

Arrived this morning from FLO, a GEM45 (no encoders or guider but incudes iPolar). Its manageable to carry out, especially if I take off the counterweight first. The weight was the deciding factor over the obvious alternative which I think I'd struggle with. Just need some time to workout how to control it before the next clear sky, oh plenty of time then.......

A very nice for a final bow. I need to go back and have another go at my own processing of this one and see if I can make it pop a little more like yours.

looks good to me, nicely composed and little noise for only 3 hours. I do like the l-enhance as well. When the next clear night arrives do you add more time to this or go for another target? Not an easy choice given what you have shown us.

What I did..... First I added computer controlled "go to" using my laptop, Stellarium and APT using All Sky Platesolver. All free and really helped to find a target. Attached are some notes I made which might help a little (not well structured - I was going to write it up neatly but never did). Then I added a focuser, helped a lot as I never had any success with the Bahtinov mask. Finally I added a guide camera and scope. That did guiding and worked with Sharpcap for Polar Allign. I will look at a RPI solution at some point as it will make me mobile to escape (a little) the light pollution. That or the ASI. At the moment though I'm ok with my laptop and you could try out the first step with very little expense. mount control notes.docx astrosetup.docx

Rather drastic! Planning to go out again tonight? and did you make it before the clouds came back?

You could look at telescopius and see the size of the image you get with different focal lengths. I'd go with the 400 I think but the 200 is going to be more forgiving of poor tracking. Not that my own guiding recently has been anything shout about! Generally more total exposure is better but I'm guessing from the mention of Exmoor that you have low light pollution in which case your 200 subs might be ok as Andromeda is quite bright. Have a look at https://snrcalc.vercel.app/calculators and it will give you an idea of the signal to noise ratio you can expect from your total exposure.

I have been aligning using Sharpcap for a while and find it straightforward. the Difficulties are really with the mount elevation bolts and not the software. I do find that when reviewing guide logs PHD2 reports a much worse alignment than I achieved with Sharpcap. For example last night I got 34" which was classed as good while PHD2 reported errors of 5' at on point and 16' at another. The previous night I achieved 25" (excellent) and Sharcap reported 1.5' on the best 3 hours of the session. The mount is on a solid base (concrete slab patio) so I dont think there is a problem there. Maybe the mount isnt helping. I'm not especially worried about it but I'm sort of curious. Does anybody else see differences like this?

Original data was 225 subs of 120 secs each in two sessions, I think I let DSS pick the best 75% of them. It didn't look any different to Pixinsight stacking all of them (at least not obviously to my eye). DSS is a lot faster for me. The framing wasn't quite right which is why I cropped the way I did but the original could grow on me after reading Alacants's comment.

Impressed that you can push the mount that far. Nice image. I'm loosing faith with my mount and considering either a GEM45 or an EQ6R Pro as a replacement so a useful post, thank you.

Thanks, I appreciate the comments. I'll have a go with Affinity, I stopped my photoshop subscription as I didnt think I needed it.

About 6 hours of data, but poor guiding which I suspect may be the reason for elongation of the stars. I'm not sure yet if I should give up on the mount or try and sort it out. Always something to learn.... Autosave.tif

How about reflection on the lens? Though I like the idea of aliens more!

At last two clear nights after I dont know how many cloudy nights. My guiding was terrible, RMS never got better than 3" (0.8px) so I had low expectations. PLEIADES_DBE_BN_PCC_DN_STR.xisf

Yep, NGC2244. Nice image, I like it. I'll be very happy to get as good a result. I'm due a couple of clear nights after who knows how many cloudy ones and the Rosette is on the list for a few hours of imaging. Fingers crossed!

I have a filter drawer in front of my camera so just to be careful I wrap a scarf round it for taking darks. I dont know if it helps, I should probably check, bright room vs dark room and see if I can see any difference. Something to do while waiting for the clouds to clear.

Lots of good points here. Desktops are normally less expensive, easier to upgrade (longer life) and more power per pound, modern linux based systems can look very like windows to the normal user (and you dont have to pay for windows). There is amazing free software about for processing. You could choose a normal hard disk and replace with a SSD in a year or two as an upgrade. A lot of the choices come down to a trade off between ease or use/set up and cost and my priorities probably don't match yours, eg I'd be happy to change a disk while I'd not like to dismantle a mount.

I have an Intel i7 processor, 32GB ram and a 1TB SSD in my laptop plus a separate graphics card. What you need depends on how much image processing you want to do. Some Pixinsight steps still take a long time, say an hour. Image editing benefits from processing power, RAM and a good graphics card but you can work effectively with a lower spec than I have, part of what you pay for is a bit of future proofing. I wouldn't go less than i5, 8GB RAM, 512 GB SSD and integrated graphics but I'm sure there are lots of people who work quite happily with less. I'd definitely go for SSD (Solid State Drive) but a separate place to store all your light frames after working on them might be useful as they use up space very quickly. AMD are good processors so if you find a suitable package with one it should be fine. I've had them in the past without problems.

I've commented before that we need to enjoy the journey, the whole experience of learning something new and understanding what might help improving the images we produce. There is enough to learn to keep me going for the rest of my life probably. My wife cant understand why that slight improvement in the image is worth buying that new camera (so I wont worry her about it). For me I can learn about the physics and why the signal to noise ratio is so much better as well as learning how to improve processing to take advantage. I agree about 'value for money' though Using the tripod and camera you already have to capture the Orion nebulae is always going to be better value than using expensive mounts, scopes and cooled cameras.

I used to stack nef files from my Z6 in Deep Sky Stacker before getting a cooled camera. I dont know if there have been format changes with your Z50 but it would be easy to check and its less work than processing in lightroom first.

I donated and got a link to the macros and then emails every time there was an update, the last one today. Drop him an email.