iantaylor2uk

I looked online and found a planewave 24" OTA (https://planewave.com/product/cdk24-ota/) for $63,500. Assuming they need to make a margin on this of maybe 20% or more, this would suggest the cost to manufacture such a scope would be between $40,000 to $50,000. You can get a 20" f3.6 mirror from TS-Optics for around $3000 (https://www.teleskop-express.de/shop/product_info.php/language/en/info/p9073_TS-Optics-20--Newtonian-Primary-Mirror-f-3-6-made-of-fused-quartz.html). I plotted a graph in Excel of approx cost of mirror (I assumed a 20% profit margin so took this off to get the approx manufacturing cost) versus mirror diameter, and by extrapolation I came up with a rough estimate of the cost of an 800mm mirror (32") to be around $5500 - does that sound about right? So, somewhat surprisingly to me, it looks as if the cost of the mirror is only around 15-20% of the total telescope cost. Or are these estimates way off?

I usually dither every 5 or 6 mins or so, so this could be as little as 2 subs (my max exposure time is usually 3 mins with an L-Enhance filter) or as many as 10 or 12 subs (if I'm down at 30 sec exposures). I also try to make sure the dither is 10 pixels on the main camera - you need to work out how many pixels this corresponds to on the guide camera.

I just picked up a Lacerta 2" Herschel wedge earlier this week. Just had the chance to play with it, and below is a single frame from a ZWO 071 Pro camera attached to my Takahashi TSA 102 f/8 refractor. I used a polarizing filter and a solar continuum filter (and a UV/IR filter too) for this shot.

When I had the scope I didn't do any planetary viewing or imaging but the moon was good through the scope. I took some photos of the moon and of some DSOs which are on my blog (in 2021)

My old Orion Optics 12" f/4 was recently on sale (as a dobsonian) on UK Astro Imaging for around £450. 900 euros is high, but on the other hand how often do scopes like this turn up second hand? Getting something like this sent through the post from Germany would be risky and you might be hit by import duty too.

I have a Lenovo P11 Tab which I use for my ASI Air Pro which I have find to be good.

Not tried Affinity for stacking yet. I find DSS pretty simple to use and it's fairly fast at stacking (I use a gaming PC with 16 Gb RAM which also helps!). I'll try stacking on Affinity and see how it compares.

I use Deep Sky Stacker (DSS) for stacking and Nebulosity or Affinity for image processing. Nebulosity is free now and Affinity is quite cheap.

I used to have one of these and I think it weighs closer to 14 kg. I used it on a Losmandy G11 which coped with the weight easily but it still was prone to the wind when guiding. You will have problems if you under mount it, especially if you plan on taking photographs with it.

I'm a bit late to this! Below is a photo of my TSA 102 (which I bought from dweller25 last year) together with a photo I took with it at the end of August. This is pictured on a Losmandy G11 mount but I'm now using it on an RST-135 mount.

Not got any direct comparison images as the last time I used the Sony A7III for astrophotography was about 2.5 years ago. The 071 camera is quite old now so I wouldn't recommend getting that now, unless you can pick up a cheap one second-hand, but the 533 could be a good option.

I tend to use high gain on the camera when I use the L-Enhance filter (max gain on the camera is 240, and I use a gain of 200). This is partly due to the fact that the Tak TSA 102 is slow at f/8. The noise will be lower at higher gain, although the dynamic range is lower, but you recover some of this when you stack multiple images. Hope this helps

A single light frame is shown below: When I analysed the above frame with ASTAP, it gave a limiting magnitude (SQM) of 18.45, so I guess I'm in a Bortle 7 zone. I was using 3 minute exposures due to the use of the L-Enhance filter, if I was just using an IR/UV filter my subs would have been 1 minute or so. If you want a go at processing the stacked image from DSS, it is available for download from: https://drive.google.com/file/d/11I9auSdK3yzWncwETfUV0JiBh9ji5ooq/view?usp=sharing I should have added that a great advantage of a dedicated ZWO astro camera, as far as I'm concerned, is that you can use an auto-focusser, and streamline all your workflow through use of an ASI Air Pro, which has greatly speeded up the whole process of astrophotography for me (autofocussing in 2 mins or so, polar alignment in 2 or 3 mins, plate solving to centre and frame target in less than 1 min, and then starting autoguiding in less than 2 mins). I mainly use my Sony A7 III for normal photography nowadays.

Below is an image I took last week of the Eastern Veil nebula with my ZWO 071 camera (stack of 54 three minute exposures), using an L-Enhance filter on my Takahashi TSA 102 f/8 refractor. I think this is better than I could achieve with the Sony A7III

I have a Sony A7iii and it is pretty good for galaxies and globular clusters etc. but a dedicated astro camera would be better for nebulae. I went for a ZWO 071 MC Pro camera and usually cool it to 0 or -5 C. As far as I'm aware the star eater issue was with earlier versions of the Sony A7 camera.

I'm trying out an 8" Newtonian on the RST-135 mount tonight (hopefully there will be some clear patches). I put a counterweight on but not sure this is needed. I also took a video showing how the mount handles the scope which is on YouTube at: https://youtu.be/H3B8Xes7zvoon

Sounds good - what guide camera are you using? - I previously used a ZWO 120MM mini mono camera but recently upgraded to a ZWO 290MM mini mono - with the new camera I use in bin2 mode and it is much more sensitive and there are many more stars in the FOV for the multi-star guiding. If you have high DEC backlash maybe the spacing between the worm and worm gear needs adjustment. I think there has been some discussion of this issue on the Losmandy forums. The view there, as I understand it, is that the value found by PHD2 is not that representative, and once you start guiding it becomes less of an issue. I saw values for DEC backlash as low as 0.9 seconds and as high as 3 seconds on my G11 and it never seemed to make much difference to the guiding.

Hopefully you did relubricate it at some point in those 20 years! I tend to relubricate my G11 every 2 or 3 years without taking the worms off by pressing a toothbrush soaked in degreaser against the worm as it is turning, and then leave it to dry, then regrease the worm and gear wheel all the way around. Mine still has the two piece worms, and I'd definitely be interested if the one piece worm makes a difference.

Thanks Chris - I've found that the higher gain is OK for the 071 camera (max gain is 240, and I am using 200), and since I am using a slow refractor (f/8) it saves imaging for longer. My single subs were only 180 seconds, and I got a reasonable result with only 2.5 hours of imaging. I know that the dynamic range is worse at higher gain but on the other hand the noise is a lot lower + you get some of the dynamic range back when stacking multiple subs. You could always try some sessions at higher gain with the 533 camera and see if is OK. My exposure times are usually three times longer when using the L-Enhance filter. If I am just using a UV/IR filter I would typically only take subs between 30 and 60 seconds (although in this case I may drop the gain down to 90 - which is unity for this camera and go a bit longer, maybe up to 120 secs). Incidentally, if you want to look in more detail at the photo, the full frame bitmap of my image can be accessed at: https://drive.google.com/file/d/1BrdOp55rXIeYO58z-3b89dCf1hgLgT0q/view?usp=sharing

Nice image - as it happens I also took a photo of this target last night. I used a Tak TSA 102 f/8 refractor (focal length 816 mm) with 1x flattener and L-Enhance filter, on RST-135 mount, a ZWO 071 MC Pro camera (with gain = 200 and 180 sec exposures, cooled to 0 C). I got about 2.5 hours of images. Inititally processed result (using DSS and Nebulosity 4) is shown below. I tend to push the gain up when using the L-Enhance filter.

They now make them with one piece worms, and they have high precision brass worms, total periodic error should be +/- 5". Check if the mount has stepper motors or servo motors. The new G11s have servo motors whereas the older style push-to mounts had stepper motors. You need the servo motors if you going to slew in a reasonable time.

I have a G11 and you can get total RMS down to the 0.5-0.7" range fairly easily but it would need a lot of tweaking to get much below this. However there's quite a long drive train on the G11 and if anything gets slightly misaligned the periodic error can go up and the guiding can suffer. It's pretty easy to change the bearings that support the worm. Mine, and probably the Celestron mount you are looking at, has the two piece worm, and it is possible to upgrade to a one piece worm which could be better for guiding. Given you can buy spare parts from Losmandy it should last many years. I have been using an ASI Air Pro on mine and it works well.

Maybe they are using higher gain values on their cameras.

I think this is debatable - most modern theories of everything believe space-time is emergent, so there could have been a time at the start of the big bang when space-time did not exist.

You don't need GR to model how to launch something from the earth into a position in space where gravity is negligible, Newtonian physics is good enough. It is an assumption that the energy of something in empty space (that is not moving relative to you) is zero, and so this is why the gravitational potential energy is negative.