Rustang

1 hour ago, Adam1234 said:

It was! And so relaxing too.  I was ecstatic to see the meteors. Not that I've not seen them before, I used to see loads when I was younger and used to go fishing at the back of the Isle of Wight where it's pitch black.

The simplest of things in life are the best. I've enjoyed every one I've seen and will always have the most amazing sight I've had in regards to meteors a few years back, engrained in my mind forever. 

Sounds like an amazing night. 

6 hours ago, newbie alert said:

Are you the one that had the accident with the scope and the cat?

 

Yeah that's me! 😒

44 minutes ago, Xiga said:

Nice one Russ.

We have very similar kit. Mount, scope and filter. Only my camera (Qhy268m) is different to yours. I shot Sadr a couple of weeks back and saw halos with my Ha filter, so will be interested to see how you get on. 

Thanks, I've had to 'tame' shall we say the halos in post but they never been to much of an issue to deal with but if these new Ultra Band's do away with them then even better, at least that would be one thing off the list of things I have to contend with! 😁

48 minutes ago, newbie alert said:

Looks great, what's the rest of the kit that you're using?

Cheers, shame its really noisy but it was only a quick test anyway.

Kit is SW80 ED DS Pro and SW HEQ5 Pro Mount.

Good idea, I will try that soon hopefully 👍

So I was finally able to get out last night to first test the second hand focuser that Steve Kindly sold to me and helped me set up so I could see if my scope was back to where it was, and to also see what my new Baader 3.5nm filter performs like. If you excuse the incredibly noisy image due to the stack only being 30mins (well i hope its because of that!) then I think its safe to say its pretty darn good in a bortel 6 location! They are CMOS optimised but stated to be excellent for CCD cameras which is what I have. Ive also ordered the OIII

In regards to the scope being back to normal, the stars do seem pretty much like what they were before the incident so I'm pleased about that, my guiding needs sorting to fully check though.

Thanks guys, I think your right, it just got confusing reading that the scope had back focus but I think you have explained what it probably means. Vlad had pretty much explained and calculated the above to me but I've only got myself to blame for re confusing it so thanks for all the confirmation 👍

1 hour ago, tooth_dr said:

@Rustang what scope are you using? I haven’t come across a scope with a specified back focus distance unless it has an integrated flattener.  In which case you don’t need the other flattener.

You are correct that the camera is 15.5mm plus 22mm for the filterwheel.  The filters thickness is multiplied by 1/3 to get the additional back focus ie .7mm in your case.

123 - 15.5 - 22 - 0.7mm = spacers needed.

Does that help?

Thanks Adam, yeah that helps, just need to see what I'm missing/not understand in regards to the scope back focus then. I'm still using the SW 80 ED which I had posted a thread about in regards to the stars in the corners, they seem to be traveling around the outside of the image and this could well be as I've seen on the web, the sensor being to far from the reducer.

How to Set the Back Focus for Your Telescope (Guide) (optcorp.com)

In regards to the scope I'm considering getting is the TS optics photo line 80, its 2ich flattener (TS Flat 2) is stated to have a back focus of 123mm for the 480 focal length and the scope has a stated back focus of 170mm from the thread on the back of the scope. 

Teleskop-Express: TS-Optics PHOTOLINE 80mm f/6 FPL53 Triplet APO - 2.5" RAP Focuser

In my research into a new scope and what I may need, I've come across something else I need confirmation on my understanding of. You know me and this hobby, this seems to be the case with most of it! 😄

So if a scope has 170mm of back focus, the cameras sensor needs to be 170mm from the back of the scope to obtain focus, correct? So where I'm getting confused is if then the field flattener has a back focus of 123mm where does that then sit in regards to the back of the scope/ camera sensor?

The sensor in my camera (QHY-9) I believe is 15.5mm from the front of its casing, then there's 22mm of filterwheel so I'm already 37.5 at the casing of the filter wheel, would I then need spacers to make sure the field flattener's glass is 85.5mm away from the camera sensor then ? 

Also I have read you need to take into account filters when calculating back focus? Can you confirm what the calculation is? I believe my Baader 1.25 NB filters are 2mm thick.

This will also help with my current setup as it appears with the stars direction of travel going 'around' the edges that my sensor is to far from the reducer.

Amazing once again 👏 👏

On 04/08/2021 at 14:46, Clarkey said:

Just come across this thread.

FWIW I use an ED80 with the 0.85 FF/ reducer with an ASI1600 which has a 22mm diagonal (so similar). Even with the 31mm unmounted filters I do get some vignetting so I suspect you may get some with the 1.25's. It is claimed that the 31mm versions are good down to F2 - but I am not convinced. What is the distance from the sensor to the filters on the QHY camera? As you are using a different reducer the image size may be smaller, but the Altair does state 38mm clear aperture so it should be enough.

There is a post about it here:

 

Thanks for your reply, only just seen it. I've not measured the filter to sensor distance, the camera is directly attached to the filter wheel so I doubt I Could bring the filters any closer anyway. I'm thinking it's the filter size because I can't see it being anything else unless it could be the Altair 0.8x reducer but I doubt it. There's some talk on whether this camera needs 2inch filters which I think it probably does unless you can get the filters 1.25 ones closer to the sensor. 

I'm surprised you get vignetting with with the ASI 1600, I was looking into getting one to hopefully get rid of the vignetting and also help bring down my sample rate! But as you say with pretty much the same sensor size il probably have the same issue, I had forgotten to check that when researching. 

49 minutes ago, ollypenrice said:

Because I haven't ranted on here about Crayford focusers in several years, and because I'm getting mellow with old age,  I'll just say that I would always choose a rack and pinion focuser over a Crayford if possible. Of the many Crayfords I've used, including Baader and Moonlite, none has been without issue. Finding the compromise between sufficient smoothness and sufficient grip is the problem, made worse by the heavy cameras I mostly use. The Crayford was designed to carry eyepieces, not heavy cameras.

There are ways to refine your guiding without spending a penny, too. You may know them but here goes.

- Running the mount slightly east-heavy by adjusting the counterweights outwards when they are east and inwards when they are west tends to stop the RA from oscillating across any backlash in the gears. The worm will always be pushing the wheel.

- Using the Guide Assistant in PHD and applying its recommendations is often conducive to better guiding.

- Experimenting with different durations of guide sub is interesting. I've found no one duration suits all mounts. Three or four seconds is fine with our roller-drive Mesus but I've gone as short as 0.5 sec with EQ sixes and an Avalon I had also thrived on subs shorter than those recommended by the maker. It used to be argued that very short subs gave a good graph because the scope was locked onto the stellar image, but that the stellar image itself was moving around due to the seeing, so the true guiding was not so good. This was called 'chasing the seeing' but, more recently this claim has been contested. I have to say that short subs seemed to work for me with the EQ6.

Olly

Thanks Olly, I have been looking more so at a rack and pinion but will probably not get one for the 80ED. If the replacement focuser I got off Steve works, which is still an 80ED focuser, then I will leave it as is and choose and upgraded scope as I'm still considering one, with a rack and pinion. it appears after chatting with Vlad (thanks Vlad) and understanding the PHD2 readings with the correct calculations, my guiding is worse than i thought, as I need to be at 1.1 arc secs and I'm normally 1.49 approx and over!! Vlad has also giving me somethings to try and I wont be spending out on anything just yet as Ive got lots to work out and try first! Thanks again for spending the time to give some advice.

43 minutes ago, Budgie1 said:

On the standard SW focuser there's a M56 thread on the end of the focus tube that the 2" eye piece adaptor or (in my case) the reducer/flattener screws on to. On the upgraded focuser I linked too, it doesn't have this thread and I had to get a 2" push-fit adaptor to mount the reducer/flattener to the scope.  

I think you'll be pleased with the belt mod. I fitted it to my new HEQ5 when I got it and it takes out all the play in the drive motor gears and reduces the noise. It took me a couple of hours to fit and I highly recommend getting the pinion extractor tool. You may only use it once but it's worth it because you'll be hard pressed (pun intended ) to get the gear off otherwise.  

I see, thanks. I have an upgraded holder on the end of my focus tube which was threaded on so I guess I wouldn't be able to use that then! Do you think the belt mod would definitely improve my guiding too!? 

4 minutes ago, Lee_P said:

I can't help with the technical side of things -- happy to leave that to Olly! -- but in general I'd say that if your stars aren't showing any trailing then don't stress over the mount / guiding too much. Sure, things can always be better, but there's something to be said for appreciating when things are "good enough" -- this allows you to focus your attentions (and money!) on another area to improve upon which may actually have a greater impact overall.

Cheers, totally under stand that and yes to me considering now how bad my mount is tracking, the stars have, to me, seemed ok, no trailing. I would still like to look at the opportunity to do something to aid its guiding though, Ive been reading the RMS wrong and where I should be at 1.1 and thinking I was always at 0.7 or under, I'm actually mostly at 1.49  and above! Its all going into the mix of what's in the pot to spend and I had already decided it's probably likely im keeping the mount so a tune up wont hurt as the mount is getting on now.

8 hours ago, Budgie1 said:

If your 80ED turns out to okay with the new, second hand, focuser, what about a focuser upgrade for that scope?

I upgraded the focuser on my 100ED to one of THESE, which I got from another member on here. It feels much more robust & better quality than the standard focuser, is easier to fine-focus and has a built-in rotator. The only drawback is that it doesn't have a thread on the end, so is push-fit only, but does have a clamping ring inside (rather than relying on just thumbscrews). It feels very secure with my SW Reducer/Flattener & ASI294 on the back of it.

Now I've got an 80ED to go along with the 100ED, I'll probably swap the focusers over later in the season and put this one on the 80ED, as I think that may get more use.

Thanks martin, its worth considering, what do you mean by it doesnt have a thread on the end!? I've got other things that need sorting aswell now as it turns out Ive been reading my guide RMS error wrong so actually mu guiding isant that great so looking to get my mount belt modifiedand tuned then I can turn my attention back to the scope to either upgrade or modify if it turns out to be ok!

So after some reading I think Ive understood it a little better and Ive also only just realised I'm not at 480mm fl Im at 510mm fl 🙈

From from what Ive read online it goes like this:

5.4 / 510 x206.3 = 2.2 arc seconds per pixel for my QHY9. Guide camera = 3.75 / 225 x 206.3 = 3.44

If I have a RMS of say 0.7 its apparently goes 0.7 x 3.44 = 2.41 then 2.41 / 2.2 = 1.09 pixel RMS error on final image so if my QHY-9 's arc seconds per pixel is 2.2 and my RMS calculates to 1.09 then is that well with in tolerance!?

this is the online paragraph that I got the above calculations from above-

"– First of all, please bear in mind that you can have a pretty ugly looking guiding graph that produces little or no visible effect on the actual image. The opposite is also true of course! You need to convert the pixel lines on the vertical scale and/or the RMS error to arcseconds of error by performing the guider pixel scale multiplication described above. Now compare that to the pixel scale of your imaging rig. You may find that what looks like a major guiding issue is actually less than a pixel or two of error on your final image.

For example, looking at the RA error in the graph above:

0.2 RMS pixels error x 2.67 arcseconds per pixel = 0.53 arcseconds of error on the guider image

0.53 arcseconds of error / 1.9 arcseconds per pixel imager scale = 0.28 pixel RMS error on final image

25 minutes ago, ollypenrice said:

Perhaps someone else could come in here. I'm not imaging at the moment and can't remember what PHD tells you about the RMS units. From memory I thought it gave the RMS in arcsecs if you'd given it the guider pixel size and FL, as you have. (To be quite honest my guiding has been so good for so long that I take little notice of it and have a rusty memory of troubleshooting. The joys of using Mesu mounts!)

If it's giving you the error in terms of pixels at the guider then you just have to mulitiply the error according to the difference between guider pixel scale and imaging pixel scale. (If your guider runs at 4"PP and your imager at 2"PP then the error 'seen' by the imager is twice that of the guider. In this case you'd be looking for an RMS at the imager of 1 arcsec, requiring an RMS at the guider of half that, so 0.5 pixel at the guider.

In the end, if the stars look tight and round then you're getting decent pictures. However, round stars are not a perfect indicator of optimal guiding because, when the RA and Dec errors are equal, as they may well be with an autoguider, they can be blurred equally in all directions. When calibrating the first Mesu we had here we alwys had round stars but, as we refined the PHD parameters, they became significantly smaller.

Olly

Thanks Olly, I'm going to go and bang my head against a wall for a bit then il look into it! If it is reading in pixels then I guess my guiding isant as good as I thought but I also guess that if Ive been happy with my stars then it must either be just on its limit or I'm lucky! To me my stars look round, well in then centre anyway!! fairly crisp but that's about all I know about what a good star should look like.

1 hour ago, ollypenrice said:

Care needed, here. You can't just eyeball a guide graph and learn anything. Using an off axis guider in a large reflector our guide graph looked like the Himalayan skyline but the true guide performance was stunning, around 0.3 arcseconds.

You say you have an RMS of  0.7 but have you fed your guide camera pixel size and and guidescope focal length into PHD? If you have, then 0.7 is quite good and will support a sampling rate of twice that, so 1.4 arcsecs per pixel.  But (this is very important) if you haven't fed that info into PHD then the 0.7 will mean an RMS of 0.7 of a pixel at the autoguider. Given the short FL of most guiders, that will translate into a much larger error than 0.7 of a pixel at the imaging camera.

So are you dead sure your RMS is being recorded in arcseconds rather than pixels?

Olly

There's really still so much I probably dont know but should know and thought I had worked out by now! Its pretty overwhelming this hobby and I'm surprised Ive even got this far!

So I worked out what RMS error I can go up to by the following-

QHY 9 mono - pixel size 5.4 so 5.4 / 480fl x 206.3 = 2.3 arc seconds per pixel-  then 2.3 / 2 = 1.16 so I gathered i can be 1.16 and under at 480mm focal length. I'm pretty sure the correct guide camera pixel size and fl have been entered correctly but looking back at an image of one of my sessions, next to RMS Error at the top, in brackets is (px): so reads RMS Error (px): which I'm guessing is not good then if that pixels and not arceseconds!?

For me this has been an incredibly hard hobby to take on with everything to learn and think about, so I have learnt the minimum which has been hard enough and just used that to get by and never ventured out of that comfort zone, so I have taken the RMS and the fact my images appear ok that all is well with guiding, if its not and that RMS error is not showing the correct reading, would I have not seen something wrong in my images!?

Pictures below of guide camera settings that were originally entered into PHD2

56 minutes ago, ollypenrice said:

Here are a couple of images scandalously undersampled   at 3.5 "PP.  

https://www.astrobin.com/383965/

https://www.astrobin.com/301531/?nc=&nce=

On widefield targets like these you can be undersampled and still get results which I think are nice. On small targets, though, the only way to capture fine detail is to use a finer pixel scale, somewhere around 1.0 "PP. You can go for less but will the seeing not blur out the extra detail? It probably will. I wouldn't get hung up over the difference between 1.8 and 2.7"PP.

Nor would I get hung up on the HEQ5/NEQ6 business. There is no evidence that I'm aware of to suggest that one is more accurate than the other.  The six just has a bigger payload. Individual examples vary considerably so either could be more or less accurate than the other. Before making the fatal mistake of fixing something that ain't broke, check your guide stats. If PHD knows your guide cam pixel size and guidescope FL it will give you the RMS in arcseconds. The RMS in arcseconds should be no more than half your sampling rate in arcsecs per pixel. So if you are getting an RMS of 1 arcsecond while imaging at 2"PP you are fine. A good HEQ5 can often manage 0.5".

Olly

 

Thanks again Olly, all good to know. Great images by the way!

Although my guide graph looks bad most of time, as I say the total RMS is always under the 0.7 something which I calculated for my set up, the best I've had it is 0.28 so not bad for the un modified old girl, best £400 I've spent so far! Yes a smooth graph might look better and I'm sure I could do some tweaking of settings somewhere but I don't won't to fiddled and make it worst, I would rather get it modified/tuned professionally, call it a service as I've done nothing in the nearly 3 years of owning it. At least if done professionally, they know what they are doing then it would in theory be ready to go, il probably make it worse! The only time I would consider the NEQ6 is for the greater payload as you say. I've got some thinking to do. My main other issue is this vignetting to sort. Would be nice to have an easier run on things when out on a session and the processing after and hopefully that will be the case in time. 

The CCD calculator seems to show that a longer focal length is better for my camera, the 600mm of the SW 80 ED being the better at 1.86, with my reducer its 2.18 which is slightly under sampling in ok conditions. The Askar 400 is the worst at 2.78 and the WO GT 81 is not as bad but still at 2.33. It appears I'm pretty limited to focal length then with my current camera.

4 minutes ago, Lee_P said:

https://astronomy.tools/calculators/ccd_suitability  <--- Scroll to the bottom and put in your potential telescopes and cameras. Then you'll get an idea of what's a good match.

My memory often fails me, I forgot there were these kind of calculators 👍

3 minutes ago, Lee_P said:

Lots of example photos on my website. You would be able to get a higher quality instrument if you were to spend your full initial budget though!

Its that difficult situation of buying to future proof yourself but also trying to spread the money you have as far as you can!  

5 minutes ago, Lee_P said:

Haha, well I figured it would be light enough so that you wouldn't need to change your mount; and sufficiently below budget that you could afford to invest in other upgrades

Its a good choice to consider, I just cant get my head around all the tech stuff to see if it would be a good upgrade, my brain just goes, smaller aperture, not a good upgrade but i know that isant the case I just wish I fully understood the in's and out's of why!

1 hour ago, Lee_P said:

This doesn't quite match your specification so perhaps isn't helpful, but I upgraded from a SW80 ED DS PRO to an Askar FRA400 and found it to be a big step up.

I guess at 400mm it would give me a little more room than 480mm so I could cut off more of my crappy vignetting corners!!