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Also, when I was testing the focus of this scope using a bahtinov mask, I noticed that - after I reach focus using red filter and then switch to a blue filter, the star pattern became slightly out of focus. To me it suggests that all lights are not focused on the exact point although the objective lens claims to be a "triplet ed". Is this normal for all apos? I would expect apos should be able to focus all lights at a focal point, as this is how they're designed to be.

Finally got a chance to try out this unbranded refractor. I took on NGC6888 with Altair Astro field flattener and Ha filter, with 5x 15min subs. Looks good enough to me. The field flattener may not be adjusted to its best spacing though.

Hi Geoff, Thank you for your reply. I understand all your points and I have actually tested against the possibilities you mentioned. I understand that speed 1 - 5 can be very slow, however what I did is to disassembled the motor and gearbox and check their rotation directly. What I noticed was that at speed 6, I can see the gearbox output shaft is indeed rotating, although slowly. But when I change to speed 5 or lower the shaft stopped completely while the motor's encoder is still running, suggesting the motor shaft is still rotating. So I guess maybe there is some coupling issue in the gearbox. Also it's very strange that the same condition happened to both RA and DEC motors. I don't think this is firmware related as I can see the motors are running as per demand. I'm really confused. I have emailed Celestron and I'll see if they can pinpoint any causes.

No replies?

I have a Celestron 127SLT with its computerized Alt-Az mount, I think this is the same mount for a series of small Celestron scopes like 102SLT, 114LCM etc. I used the mount for another scope of mine, but this scope is a bit heavier and may have overloaded the mount. Recently when I was trying the mount out I noticed that the slew is acting weird. When I select the slew rate between 6 - 10 the Alt and Az axis can move with no problem. However when I select any slew rate between 1 - 5, both axis are unable to move. I took the mount apart and examined its components, both motors are working normally - the motor speed changes when I adjust slew rate between 1 - 9. I found that it is the gear box between dual axis motors and Alt/Az rotating gears that is faulty. At slew rate 6 - 9, the out shaft of gearbox rotates with motor rotation, but at rate 1 - 5 the gearbox shaft stops rotating even if the motors are still running. I suppose this suggests something wrong in the gearboxes. How can I fix it? Any ideas? Thank you for reading.

Agreed. I forgot to crop and distortions as being in a rush.. I even forgot to crop out the stacking artefacts!

Just out of interest, why is apo with (relatively) low aperture gives best results in such conditions?

First time trying out narrow band imaging (Ha), and I chose NGC7380 as the target due to its very high position in sky and the cool name. I'm using Skywatcher 150pds and Atik 314 camera. Total exposure 7 x 20min. Overall I'm quite satisfied with the image, although there are some coma at the corners and edges, and I can feel I'm already attracted by Ha narrowband imaging.

Thanks guys, for the advice. So it seems I was bit unfair with judging the 127Mak... I don't think the scope temperature is fully stablised as I used the telescope in the same room that I stored it (I left the backyard to astrophotography). I do realise Jupiter is quite low in the sky and would expect some influence considering the atmosphere. Also 6mm is a bad choice.. I would definitely try with some other magnifications later on. I think I phrased the title wrong - I'm not saying 127Mak is a bad scope, I knew it is excellent when I was watching the moon. I think what I mean is I was a bit disappointed with using the scope to watch Jupiter at such non-ideal conditions. Thanks for the chart, John, that's very good piece of information. Lessons learned! - should've considered more factors before drawing conclusions.

Clear sky this evening (finally!), after I set up my astrophotography equipments and started tracking, I decided to do some visual observation on Jupiter in the meantime with a Celestron 127SLT Maksutov Cassergrain. I haven't really had a good use of this Mak before as I bought this mainly to bring little family members (nephews) into astronomy and have only used it to view the moon for some times. I am using a TS 6mm planetary eyepiece but am surprised to find out that I could distinguish any details on Jupiter. From the eyepiece it is just a blurred orange disk. I used to view Jupiter with a Skyliner 200p and the view is awesome with crystal clear bands and zones. I didn't expect 127SLT to give me the same view (because of aperture size) but I did expect to see at least some details. I later on tried with a 80mm apo with same eyepiece and I can clearly see the bands. I always thought 127 Mak is a nice little scope for planetary observations. I was wondering if the blurred Jupiter is because I maybe pushed the scope beyond its power, or maybe the scope itself is out of collimation? Has anyone got any experience to share? Thank you!

I tested the scope for visual last night by looking at Vega. I've noticed that the tube may be a bit short for the objective lens, as I need to roll the focuser back a lot to reach focus. Clouds rolled in quickly so I was unable to try with the ccd camera. Also there is no finder bracket on the scope which is a bit inconvenient. I don't think it's possible to know how the lens was damaged in the first place since it's an auction item. But is there a way to check the alignment of optics? I did try to use laser on the eyepiece holder and the exit beam comes out on centre of the lens. Thanks.

Thank you for your replies. I did notice that there is a little crack on the very edge of the objective lens - a bit disappointed. The rest looks all very good so far. I'll try it out hopefully this evening.

Thank you Gaz and John, the OTA does look like home made, as I noticed the dew shield rim is not actually cut straightly (doesn't look like the work from a factory). I'll try the scope out when the weather is better. But anyway I do feel it is a bargain for a £80 bid.

Hi, I recently acquired a telescope from an auction. The telescope is said to be a Skywatcher 80mm apo triplet so I bid for it straight away. After receiving it, it has blue tube so should be one of those old skywatcher models, with a dial speed focuser. Looking at the wordings around the lens it does say that it's a 80mm f7 ED apo triplet. I tried to o search for some information and specs of this telescope but couldn't seem to find any useful information. Does anyone have any idea what model this is, and is it a good scope in general for astrophotography? Thank you very much!

Thanks very much for the insights. It's a very good point - that if I were moving to narrowband imaging, e.g. using Ha/OIII/SII pallet, achromatic refractor could actually be a low budget choice. It is a bit disappointing that both luminance and blue channels would be affected - so it looks achromatic is certainly a show stopper for LRGB imaging. I'll probably just focus on finding a apo that suits me.

I'm currently using a newtonian and a very nice mono ccd camera, and am quite satisfied with the experience so far. However I'm still thinking of moving to astrophotography with refractors, for better contrast and supposedly more crystal details. But I was again and again put off by the price for high quality Apos, for the fact that even a "small" 80mm ED will cost more than twice the price of my 150mm Newt, let alone the higher end triplets with larger apertures. Recently I was thinking of the feasibility of using Achromatic refractors for astrophotography. I understand that achromatics are prone to chromatic abberation as colors don't usually focus on one point. However this can be countered by the use of mono cameras, as what I have now. So all I need to do is to refocus for RGB channel and ideally I have have quality monochrome images for each channel at a much lower cost than a Apo (although Lum frames may be affected as it contains information of all channels). I'm not an experienced refractor user so I'm not sure how plausible this idea is. Has anyone had any similar experience or even had a trial on this? Any suggestions will be helpful. If it is a doable idea, are there any suggestions for the "good" achromatics for astrophotography on the market? Thanks in advance.

Wonderful advice. Thank you William, I'll put a USB tracing pad in my ebay shopping cart now, sounds like a great idea. Thanks a lot for the tips.

I'm wondering how flats can be taken when there is a need to change focus during a session? Normally I take flats with telescope pointing to a bright wall and a white paper covered on the tube. So imagine if I'm in field and I need to take flats before moving to next filter and refocus, how should I take flat frames? I did stretch the histogram a bit too much to be honest, just personal preference really. Thanks for the advise!

Just to report back, I tried to take some flat frame to experiment the difference, and I'm happy to see the vignetting is mostly gone and the artifacts are greatly diminished. I'm still ramping up with experience of the imaging and processing, I used to think that flat frames are just for removing the image gradients, but now I understand that flats may be even more important to me since it also removes the oddities created by dusts/stains in the optic chain (as for dark and bias, the cooled camera did a good job to control the noise already). Thanks, William, for the nice tips. I did have prepared a folder of dark and bias frames at certain temperature, this proved to be very convenient. One question - if I'm to take mono subframes for different filters, do I need to take flats after each filter? Maybe a silly question, but I still haven't tried imaging through color filter yet, not sure if I need to re-focus for each filter. For comparison with previous image, after flats are included and with a some level/curve adjustment, the image does look way better.

Thanks everyone for the insights. So it looks like the pattern is from dusts in the optical chain (most likely on filter surface?). I'll try to take some flat frames later today and try to clean the filter to check if this will make a difference.

Hi, I am using skywatcher 150PDS with Atik 314L+ mono + IR cut filter. I tool 10*360s frames of M104 and stacked them up using deep sky stacker. However after processing by adjusting levels and curves, I noticed that the stacked image appears to have some weird artifacts in the shape of circles. I'm struggling to understand how they can be generated, or where these patterns come from in the first place. The final stacked image is as below: and I highlighted the artifacts: Does anyone know where potentially these are coming from? I hope the camera is not malfunctioning. Thanks in advance!

Hi, I'm currently using a skywatcher 150PDS on a HEQ5 Pro mount for mono ccd astrophotography. Recently I noticed someone selling a Equinox 80 Apo refractor at a reasonable price and I'm tempted to have one. But before that I'm trying to work out the difference the apo can bring and decide if I really should go for that. The main reason I'm looking at this Equinox 80 is that it will give me a better field of view for certain astro targets. F ratio wise, the Equinox 80 is F6.2, and with a field flattener it will be of a very similar F ratio as my current 150PDS. But because of the size of aperture, 150PDS has almost twice the diameter of Equinox 80, does it mean that I need 4x the guiding time if I'm using Equinox 80 compared to my 150PDS, to have the same luminance? Any advise on this topic? Thanks.