ollypenrice

TEC. In imaging terms those stars are not big at all, they are very small. Similarly, in imaging terms that is as close to a halo-free Alnitak as you are ever likely to see. It is phenomenally well controlled. You're looking at a deliberately under-processed image, one to which only the simplest of log stretches has been applied, since my aim is to show the native optical performance of the TEC. To see why I think it's remarkable you'd need to look at other broadband images of the Flame Nebula. (Narrowband filters hold down stars in ways that broadband filters don't, but broadband give natural colour.) I don't want to link to other people's images and say, 'Look, your Alnitak is a big white blob,' but I think you'll find plenty of big white blobs out there if you look! Olly

Life's too short to read all of a thread like that but by the end of page one I hadn't found a leaking TEC... Olly

The Tak FSQ106 is optimised for imaging but the TEC is a better imaging scope, albeit slower. Here is a pure log stretch of Alnitak, cropped, taken with the TEC in 10 minute luminance subs. As you can see, reasonably faint detail is already showing but, critically, Alnitak is cleanly split as a double. I can split it in the FSQ data as well - by layer masking different stretches together - but without fancy processing Alnitak is a big white blob. The TEC gives a clean split straight from the raw data, and note how close to Alnitak we can see structure in the nebulosity. Not many refractors can do this. Olly.

If it leaks. But it doesn't. And bacterial growth can affect air spaced lenses, too... Olly

It is primarily connected for visual, yes. Regarding its imaging prowess, there's an interesting debate. I've seen it dismissed by one CN poster as 'a glorified achromat,' an opinion I find incomprehensible. What many imagers have found is that the blue correction is greatly improved by the TEC field flattener, though the official line from TEC is that this is not true. My own experiments with and without the flattener clearly suggest that it is true. A slight tendency to bloat on hot stars disappeared with the flattener, which is a prodigious bit of kit giving a vast, well illuminated field larger than any current amateur cameras can exploit. I love it as an imaging instrument. Some samples... https://www.astrobin.com/full/335042/0/ https://www.astrobin.com/full/380941/0/ https://www.astrobin.com/full/419975/0/ We have two of them here with no discernible difference in performance. Olly

Taking a step backwards in time, we might care to remember that the original TEC140 was, if this isn't an oxymoron, a budget 'premium apo.' It was non-fluorite and sub 150mm and oil-spaced, all of which put it below the eye-watering prices of the premium 6 inch opposition, yet it ran them close. Close enough, in fact, for this aspect of its history to have been forgotten since it tends to be regarded, now, as one of the full-on premium contenders. (I'm talking about the pre-fluorite versions.) Also helping this creeping advance up the food chain was the TEC reputation for quality control and accessibility, neither of which are Takahashi strong points (though I think it's mostly the FSQs which seem to defeat Tak's best efforts to send them out in consistently good fettle.) I've just looked up the price of the current Tak 150. Had I gone for that rather than my second hand TEC 140 I would be about 11,000 euros worse off. Eleven thousand euros!!! If someone offered me a straight swap, my TEC for a new Tak 150, I'd decline because I wouldn't risk it. Olly

I've no experience of imaging in light pollution* but I remember a Craig Stark video in which he demonstrated that LP can be overcome by sufficiently long integration. This runs totally counter to the argument that LP imposes a certain limit beyond which it isn't worth exposing for longer. According to Craig Stark, the opposite is true. When deciding on exposure times I like to know why I'm going to make a particular choice and this comes down to what I'm going to do with the data. If the idea is to prize some terribly faint signal out from just above the background sky then a huge integration time will certainly pay dividends. If I'm not trying to do such prizing then four times less data will probably be fine. Conversely, if I'm shooting Ha on a bright target with little faint signal, then I know I'm going to be adding it to the red channel in Blend Mode Lighten. In this case only the brighter parts of the Ha will influence the red channel and I don't need to build faint Ha signal. Olly * Conversely I have lots of experience of realizing that I've forgotten some small thing like the salt and now have forty-five minutes of driving to go and get it!

This would depend on several things. I would agree that ten hours per filter may take you to somewhere fairly close to what's possible but that might mean ten Hrs in Ha, another ten in O111, ten in Luminance and, say, 2 Hrs per colour. It also depends on how faint the target is and, crucially, on your ratio of pixel area to area of aperture. (This is what really matters rather than F ratio.) And then there's light pollution to consider. The worse it is, the more exposure you need. We cannot, therefore, easily quantify the benefits of long integration. Olly

I'd be interested to try it but I don't find much to complain about in the original. There really isn't much room for improvement. Regarding the original question, I'd go for the TEC. For a while, some came with an own-brand focuser. This is OK but not as good as the Feathertouch, which is the more usual one to be found on the 'scope. The instrument is brilliant both for visual and for imaging. Olly

That's great. Well done. To take it further I'd be looking at two issues, reducing star size and getting more Ha signal from the existing data. Just working with a screen grab in JPEG (so a terrible way to work!) I took the image into Photoshop and ran three iterations of Pro Digital Astronomy Tools (AKA Noel's Actions) 'Make Stars Smaller' and then went into Image-Adjustments-Selective Colour and greatly lowered the cyans in red. This two-second trick is simply astonishing for getting more out of Ha signal buried in one shot colour data. I would not use these methods, or not so heavily, if working from scratch because there are more subtle and more complex ways of getting there. However, my aim wuld remain smaller stars and more Ha. I think your capture was very impressive. Olly

A late reply but I wonder if this may only apply to a well collimated camera. Perhaps a significant tilt on the chip would send the chip-cover reflection back closer to the source laser when rotated to a certain orientation? Olly

That's nice, Carole, and not badly damaged by the cooling issue. We've all done that. Ten days ago in my case! Olly

I don't process in AstroArt but do stack and calibrate in it and I used to run an imaging camera and guider in it as well. I've always liked it. Olly

If you take a warm, dry towel from the airing cupboard and drape it over the front of the tube (not in contact with the lens but resting on the extended draw tube) it will speed up the demisting process. The fabric quickly absorbs the humidity. Olly

Very few people used the original SX camera control software. Almost everyone ran it in third party software so I'd be inclined to do likewise. Olly

I very much like the image. Regarding the ultra-smooth background, remember that Photoshop will let you 'add noise.' I wouldn't discard this possibility, however counter-intuitive. Just a little grain stops the background looking like a close, reflective surface and pushes it back, psychologically, to where it should be. It's easiest to use the noise addition as a bottom layer since the layers opacity slider gives easier control over the amount than the tool's own slider. The colour select tool lets you add the noise only to the background. I'm developing a preference for this kind of M31 image. My own effort, and many like it, have concentrated on pulling up the outer regions and battling for structure deep into the core. This is all well and good but it looks anything but natural. Olly

That's a tricky one because the 1/4 inch bolt is the norm for attaching the camera and should work. Perhaps the dovetail doesn't have a flat surface where the camera sits on it? Could you add a friction washer between camera and dovetail? Or add some improvised brackets to stop the camera rotating? Olly

We all use it but the trick is to make it look as if we haven't! Olly

I meant that it's sharp in the sense of having lots of small scale detail but does not have the scratchy look that comes with heavy use of software sharpening. It looks naturally sharp. Olly

Unless it has been radically redesigned, I wouldn't go near a Tak FS60 for imaging. I've processed data from two examples in the past and both had truly abominable blue bloat. Olly

Once you have your pure background sky up to a brightness you like (which for me is about 22 in Ps for galaxies) you can pin the curve at that value and stretch just above it, restoring the curve near the top.This lets you pull out faint nebulosity without white clipping at the top. In the example below the background is pinned at its original value and the added kink, or bulge, placed in the curve affects only the fainter, outer parts of the galaxies. It leaves their cores and the stars almost unaltered. This method allows you to avoid unnecessary stretching of the background (which can lift it above the noise floor) and keeps the bright parts down while getting more out of the faint signal. It would provoke an apoplectic fit amongst the PI developers so please don't ever show it to them. Olly

Did you try to stretch the outer glow any harder with the extra data? You might find you could reveal a it more of it? What I found in going after that very faint stuff with a CCD camera (and this wouldn't apply to CMOS) was that going from 15 min subs to 30 min made far more difference than adding extra 15 min subs. Olly

Very good indeed to my eye. Excellent but unforced resolution. Olly

Hmmm. That's one to think about. The difference is that you're putting the laser beam on axis. On that basis the return beams from chip window, cover slip and pixel would, in a perfect world, also be on axis, though the pixel reflection might be offset? But what if the chip window is not in quite the same plane as the cover slip? How will you know which is which? It's the cover slip that needs to be tilt-free. Does the off-axis laser give you a better chance of identifying the cover slip reflection? Olly

I think your reservations may be justified. My impression, though I need more experience with the setup to be sure, is that a sampling rate of 1.8 arcsecs per pixel is not going to support presentation of images at 100%. A refractor of comparable focal length would be better in that respect. The question is, though, 'Does it matter?' That depends on your imaging objectives. I don't regard a FL of 400mm as one with which I'll go looking for the finest details. It's a widefield FL and, in widefield imaging, I find most of the interest lies in going deeper rather than in finding small-scale details. Obviously the RASA is at its best in that rôle. And, even at 50% of full size (which it certainly does support), the result is crisp and clean in most respects. A soft extended glow around bright stars is a RASA characteristic just as diffraction spikes characterize spider vane reflectors. All optics involve compromise and we choose the compromise which best suits our purposes. If our aim is to find faint, large scale structures which are rarely imaged, the RASA might be the right compromise. If the aim is to make large scale mosaics in which downsizing of individual panels is something we're going to do anyway, then the 'resolution compromise' disappears entirely. It's also likely to be the right compromise for the imager exasperated by bad weather and lack of integration time. Whether or not the RASA is right for you depends on what you would like to do with it. Olly