jif001

Agreed - stuff like this means that us Frac types have the best of both worlds 👍🏻

I thought I’d have a go at printing a mask for my refractor (102mm) to create those diffraction star spikes you get with a Newtonian - and it worked! This is simply a Bahtinov mask taken from Thingiverse and modified to replace the slits with a cross having a 2mm square section. The test image of the Pleiades illustrates the effect. The arrow allows for consistent alignment between sessions.

Here is a simple focus arrangement for a Red/SpaceCat based on a Skywatcher auto focuser. I bought the focuser from AliExpress for £38 because there was no stock here. The tax man and post office added £11 to that on arrival a month later so it cost £49 in the end. FLO currently (Jan 2021) has a few in stock for £45. I also bought a belt and pulley for a few quid from Amazon, plus a 5m RJ10 to RJ10 cable. Overall it probably cost about £70. if anyone is interested I’ll make the stl available but it’s a simple design to copy. https://www.firstlightoptics.com/astronomy-cables-leads-accessories/skywatcher-auto-focuser.html

I set about solving the same problem. Mine is a simple interference fit with the polar scope and I can easily swap it between my two mounts each time. It also fits my finder for the rest of the night! It’s not on Thingiverse but I’ll put it there if there is any interest in the STL. This was part of the justification for buying a 3d printer: a right angle finder for a camera is about £30, but for a telescope it’s £90 and the only difference is the adapter that attaches it! The rest of the justification was the automatic focuser for my SpaceCat, which cost me £60 instead of €250 (although, in fairness, it doesn’t interface with ASCOM).

Check the settings in the handset, particularly the date. I think it uses the American format, where, for example, August 1st would be entered as 8-1-2020 (i.e. ‘August 1st’). If you entered it the other way around as 1-8-2020 (‘1st August’) the date will be 7 months adrift which might explain it going in the wrong direction.

It’s normal for the mount to be inaccurate when it slews to the first target. You should always follow polar alignment with 2- or 3-star alignment. The latter assists the Goto system in finding the targets accurately. Pick a bright star some distance from the pole star and use the Goto to slew there. It will be off, but you use the handset buttons and finder scope to centre the star in the field of view, then tell the handset it’s there. Repeat with a second star somewhere else then, ideally, a third one. That should mean the Goto will be accurate finding your next target. if you have a computerised setup using ASCOM, you can platesolve instead of centring the star each time, and sync the location to the mount.

This may help ...

Nice image 👍🏻 Minor point though - it’s not NGC7000 it’s IC5070. Happens to be my profile pic too!

You’re welcome 👍🏻

The problem is point 3 - the word ‘up’ is very subjective. As you say, it doesn’t matter what number is in the ‘12 o’clock’ position, but it does matter that the number you choose to put there is EXACTLY in the ‘12 o’clock’ position if you want accurate polar alignment. It doesn’t matter for visual but it does for imaging.

The results speak for themselves ...

That’s indisputable, but the point of this post was not about tax avoidance. No-one wants to pay tax if it isn’t necessary, and the point was merely to clarify the issue for those who may be wondering 👍🏻

For info, just in case you are thinking of buying a Pixinsight licence in 2020: My Pixinsight trial is about to end and I found it indispensable so I’m going to cough up the cash. The website states that VAT is not payable outside the EU and since the UK is now outside The EU I expected it not to be charged, but it is. I queried it with them, and they said that by law VAT will remain payable on EU purchases until 31st December 2020 https://www.avalara.com/vatlive/en/country-guides/europe/uk/british-vat-rates.html

Images are a different size so not straightforward to merge with the rest. I'm more interested to understand why this happened so I don't fall into this trap again

I don't think I could have selected RoI by mistake. It's not an easy mistake to make, and I've never used it before so it couldn't have been somehow left in that state either. I hadn't spotted the gain, and every one of the blue pics has a low gain value like that. But why would that influence the image size? I certainly didn't alter the gain between filters so I've no idea how that happened. Individually the pictures are OK and can be stretched as normal. The gain on the others is 1. The images are all 4144 x 2822 (image editor file info dialog) and are 23Mb rather than the 32Mb normal file size. I'm out again tonight trying to get the data I'm missing from last night. Keeping an eye on file sizes as a clue to what's going on!

A strange thing happened last night. Over the past week I've been collecting LRGB data on M51, and finished last night having accumulated 7 hours altogether. Today I tried to stack them and got an error from DSS saying basically the files were not compatible with each other. When I looked closer I found that an hour of blue data I got last night has an image size of 4144 x 2822, with all other files at 4656 x 3520, including R and G collected earlier in the night. I've since discovered that every picture I took after that (other targets) had the same issue. I've just tested it again with some dark frames and it's back to normal. I'm using an ASI1600MM Pro with a 4656 x 3520 sensor, so I can't figure out why some of my files are the wrong size. The FITS header in these blue files correctly identifies the camera and other parameters such as pixel size and sensor temperature, but the image size is 4144 x 2822. Any idea what's going on here? I've wasted a precious hour of imaging because I can't now stack these pictures with the rest, and I'm keen to understand why. Another possibly useful bit of information is that I was simultaneously running two instances of APT and the other was using an ASI294MC with a sensor size of 4144 x 2822. Given the numbers that seems too much of a coincidence. Could there have been some 'cross pollination' going on here? If so then why only the sensor size and not every other parameter? 🤔

The EQ5 has a payload limit of about 9kg for visual or 6.5 kg for imaging (some would say 50% of the visual payload - so 4.5kg for imaging). That ‘scope must be about 9kg before you add anything to it, so as you have suggested yourself, payload may be your issue.

Nikon D7200. No intention to mod it though.

A few weeks ago I graduated from DSLR imaging to mono imaging with filters. I don’t regret it. It’s more time-consuming both during and after capture, but much more rewarding. My set-up includes an ASI1600MM Pro Cooled camera with an automatic 7-filter wheel. I have two scopes (refractor/Newtonian) but one mount, so now I’m looking to buy another (better) mount and having two rigs on the go. Therefore I’m also considering buying an OSC camera - probably an ASI294MC Pro Cooled. However, I could save a load of dosh by re-employing my DSLR, so should I just do that instead? Are there significant advantages in using a dedicated OSC camera over a DSLR? My preference is for a new camera, and having experienced (unmodded) DSLR imaging I’m interested in the views of those who may have made the transition from DSLR to OSC so I can decide if I’m making the right (expensive) decision. One way or the other I’ll have a camera on both scopes. One issue I expect to have is the DSLR back-focus problem on the Newtonian. Does this affect dedicated Astro cameras?

Astronomy by Andrew Fraknoi - £69 hardback, £38 paperback, Kindle edition - free! https://www.amazon.co.uk/Astronomy-Andrew-Fraknoi-ebook/dp/B075FG4KTK/ref=sr_1_1?keywords=Andrew+Fraknoi&qid=1582030552&sr=8-1

I’m not sure I trust Clear Outside beyond today. Longer-range it seems to keep changing its mind. I left work on Friday saying I wouldn’t be in on Monday, on the strength of a prediction by Clear Outside that an all-nighter was on the cards Sunday night. It seems to have overlooked Storm Dennis, so here I am in work on Monday having not even ventured out last night.

I don’t know if this answers your question, but have a look at my responses in this thread...

Yes that’s it - your starting point needs to be correct if your end point is to be correct. the red cross won’t move when you rotate RA, but if it’s in the wrong position to start with then it will always be in the wrong position. in the example the dodgy reticle red cross is aligned to a position to the left of the pole, not the right - have another look 😊 Think of the reticle as a wheel you can roll along the ground. In the right hand image below, the 6 is in contact with the ground. If I roll the wheel to the left so that the Polaris yellow cross is in contact with the ground and the broken line is vertical - i.e. it’s moved to the position in the left hand image below - then the central red cross will have moved to the left.

See if this helps ... Here I have two reticle screen shots. One has zero exactly at the top, which is what I want, and the other has an error whereby zero is not exactly at the top, and I’ve grossly exaggerated this error to illustrate the point I’m about to make (I’m not good at judging when it’s exactly vertical but I’m better than this!). Ignore the blue lines for a minute Remember, what we want to achieve is polar alignment, which means the red cross in the reticle needs to coincide with something we cannot see - the celestial pole. Luckily there’s a nearby star that we can see, Polaris, and we use it as a guide. By getting Polaris in the right position in the reticle, at the correct angle, we know that the red cross hairs are aligned with the celestial pole. An app or other means will tell us the angle we need. Look at the broken line joining the position of Polaris (yellow cross) to the central red cross in each case. In the second image my exaggeration of the tilt has made this line deliberately vertical so it’s easier to illustrate the error it creates. The true position of the celestial pole is where the red cross is in the first image, but you can see that the rotation of the reticle in the second image has moved the red cross to the left of where it should be - imagine superimposing the second image on top of the first so that the two yellow crosses exactly coincide. What you would see is the red cross of the superimposed second image approximately where my blue lines cross each other in the first image. What this shows is that if my reticle is tilted when I polar align then my scope is NOT aligned with the pole. If I used the tilted reticle below to polar align then I would be aligning with the blue cross in the first image. The real error you might get by having your reticle not exactly vertical is much smaller than this, because it won’t be this far out, but it’s an error nevertheless and will affect your tracking. Remember also that you need to establish the correct (vertical) reticle position (as in the first image) once only, and then mark your mount so you don’t have to do it again - just align the marks on the mount and you know you have the equivalent of image 1 and no tilt as in Image 2.

I can’t comment on the ‘bubble’ reticle with any authority because I have the clock-type (as above) but I’m sure the principles are the same ... if you look at the reticle screen shot above you’ll see a yellow cross. That’s where I need to put Polaris in my polar scope reticle in order to polar align. Get it there and I’m done. However, for my polar alignment to be accurate I need to know that when I do this the reticle zero marker is at the top - i.e. exactly at the top, dead centre, with the line between it and 6 exactly vertical and the line between 3 and 9 exactly horizontal. That’s something I cannot achieve by eye because my eye is simply not accurate enough. I may get zero to look like it’s at the top, but is it exactly at the top, I mean, EXACTLY? So I used the method I described - get Polaris (actually any star will do for this bit but Polaris is best placed) dead centre in the cross and then using ONLY the vertical adjustment of the mount move the star up to the circle. Having done that I know EXACTLY where the zero should be and I adjust the RA axis so that the zero in the reticle exactly coincides with the star position, then I lock it and mark the mount so that I can find this position again without using the polarscope. I can then be confident that my reticle is in the precise rotational position for aligning with Polaris when I need to polar align. All of this is aimed at finding the correct reticle position only. It’s a one-off procedure and the marks on the mount are now my reference points for getting the reticle in the correct position prior to polar alignment. The video you’ve seen elsewhere using the bubble reticle is just applying this principle - getting the reticle in a known rotational position so that polar aligning can be done accurately. You can polar align without doing this, but it won’t be as accurate. That doesn’t matter for observing where a bit of drift won’t spoil it, but if you are imaging then any drift at all is to be avoided. Let me know if it’s still not clear - I’m happy to try and explain it again if necessary because I would have been glad of some guidance like this myself and I get why it might be difficult to grasp! I’ve already suffered your frustration!