Mandy D

Wouldn't that be K/W, as for thermal resistance?

Wierd! I have just copied my Lanczos image on this page into GIMP and it has exactly the same dimensions as your original and my previously edited ones. I took great care with the dimensions each time I scaled: 498/2 = 249. Yes, I can see the difference between the GIMP image and the Lanczos one and I did compare the three times resampled one with the equivalent GIMP one and, yes, it is better, but not perfect. All the physics of this makes sense to me and should result in what you are stating, but what I am seeing is different. I suspect (as I vaguely suggested at the start) that the image processing software is the problem, not the physics. Thank you for the interesting discussion. It has certainly advanced my knowledge of the subject.

Thanks for the explanation. I will read up on all that you have linked me to, as I like to understand the science behind what I am doing. I downloaded Irfanview and ran the image through Lanczos resampling down and back up 3 times, with similar results to what I had in GIMP. I then applied a further two resamples to confirm it. The PNG file is attached. The TIFF is very similar, so I'm not posting it. Have I got something wrong? Apologies if this appears to be doubting what you say. I understand and accept your assertion that the data should be completely retained as the higher resolution was not necessary to begin with, but it just does not appear to be happening.

I find incorrect use and case of SI units really annoying! Another favorite is kelvin-watts (KW), although I have yet to figure out what property this would specify! Ahh, Mr Raygun ... Why did it never become popular to spell his name like that? I never once saw it, but thought it many times.

I understand your thinking, but was still not convinced, so I did the sensible thing and tried it for myself, but extended your experiment and repeated the process three times on the same image. Resampled to half size then resampled to full size, rinse and repeat twice more in GIMP. The result was very clearly nothing like the quality of the original. So, I downloaded your first image file and converted it to TIFF to ensure no compression was being applied and repeated the process and got exactly the same result. My final TIFF image is attached below. I'd appreciate your comments, as clearly something has gone wrong. Is GIMP applying non-linear algorithms to the process or is it simply that your process is not valid? Perhaps you would be kind enough to provide details of the software you used and maybe even run the image through it several times to verify that you get a different result to me. I've also included a PNG to save everyone having to download the TIFF. baseline_Resample_3_times.tif

Yes, I would have liked to launch him into space! It is just one of several bad experiences with Dover customs. I usually end up in their customs shed when I pass through! I'm glad your VX6L survived, but shame about the TV. I hope it was a case of "Oh well, I wanted a new one, anyway!"

I would definitely avoid Amazon for this type of purchase. Go with an established, reputable astro vendor such as FLO or RVO. There is a good one in Bordeaux, who I have had dealings with when I'm in France, but I forget the name. I don't know any in Portugal. There is the Heritage 76P, which has a spherical mirror instead of parabolic, but the views of the Moon are not too bad through it and it is only about £60 (€70) in the UK. FLO sell the 100P here, but it is out of stock: https://www.firstlightoptics.com/heritage/skywatcher-heritage-100p-tabletop-dobsonian.html

Yes, dropping is not recommended! A UK Dover customs officer lifted the back (mirror) end of the box carrying my 250PX in the back of my Land Rover and deliberately dropped it about a foot. He got a serious rocketing from me about that! Didn't budge the collimation, though, which seriously surprised me.

When I was a member of the IOP, I used to receive their magazine from time to time and the only thing I can now recall reading in it was a spoof about quantum tunneling washing machines in which socks tuneled to other dimensions, thus explaining why you could never find a matching pair. I wish I could find that article, now! Found it: https://www.mersenneforum.org/mayer/qtl.html

I did notice the three screws and figured that would be possible, but I only have that scope because it cost just a few pounds at a car boot sale and I liked the artwork on it.

Have you considered using the Windows version with WineHQ?

The Skywatcher Heritage 76 is not collimatable. I have one here and have just checked it, both the primary and secondary mirrors are fixed in place.

Given how well both my Newts hold collimation and the fact that spherical mirrors just do not match up to parabolic ones, I would choose the latter. I've never needed to adjust the collimation on my 250PX and only collimated my 200P when I got it because it was so far out, you could not even see the primary mirror in the eyepiece. Personally, I would also avoid any Newt on which the collimation cannot be adjusted. I'm sure both of mine would benefit from having the collimation tweaked, but I am happy with things as they are, right now.

Don't forget, it is all single track cart lanes with sheep roaming down them in the UK where everyone drives a Mini (the original, not the one on steroids!). Hollywood portrays the UK exactly as it is, you know, complete with red double decker buses and phone boxes. You are a pariah if you dare to own or drive a Land Rover over here. 🤣

It's unpretentious and there is no doubt about what it is. I like it. It's better than my attempts on Mars, so far.

It was very nice earlier this evening and I got some very sharp images of the Moon and was amazed at how many of the smaller craters I was seeing, not that I can name them. I was stuck at 600 mm on a full frame camera, as my back will not allow me to move the scopes at the moment.

This is especially pertinent advice in the UK, where we don't all drive around in Ford F450s. I read, somewhere, that the 1200 mm focal length that is popular on Dobs was chosen to allow the tube to fit across the back seat of most cars. I know that it even fits in my Peugeot 107, which is about as small as cars get. The base is the problem, as it has to straddle the tube as it won't fit in the boot, which is why I would normally transport it in the Land Rover.

No, I used a 300mm prime lens and x2 teleconverter on the Nikon D800. I can't move the telescopes at the momeent, due to back problems. I would have loved to get the RC on it with a x2, as that would give me 2740mm FL.

That last one is impressive!

@Mart29 Nice! You certainly have some detail there. The sky looks really hazy to me, yet we are capturing good data. I was going to go after the night-time part of the Moon, but no chance with the haze.

@Mart29 This is what I just captured.

I wasn't expecting very much tonight when I saw how hazy the sky was, but captured the sharpest image of the Moon I have managed to date. I'm just not sure that there isn't something wrong, it looks so sharp. I've done nothing more than stack the best 50% of 94 images, no post-processing at all after that. Any experienced astro-photographers care to comment?

I like the new colours, @Mart29. The moon peeking out from behind the planet is nice. I love capturing things like that. I got a 7th magnitude star just before it passed behind our own Moon a few nights ago. I've just been shooting our own Moon and will post a photo shortly. It is the sharpest I have ever managed.

I have the RVO 2" Barlow. It is fairly lightweight and comes with a reducer to 1.25" for not a lot of money. It seems to have a good reputation in here and it works well in my 200P and RC6, although I prefer my Explore Scientific focal extender, but that is nearly four times the price. https://www.rothervalleyoptics.co.uk/rvo-x2-ed-barlow-lens-2-with-adaptor.html For eyepieces, I like the Baader Hyperion, but everyone has their own opinion on this topic, so I'll leave it at that.