symmetal

Reading up on Petzval designs it says that the front doublet is designed to introduce coma to effectively cancel out the coma of the rear doublet. So that it seems is not happening on the two Redcats I've tried. I don't think that focus itself is the main problem, as even on the corners showing severe coma the stars themselves (ignoring the coma) are reasonably small. I took some blue images last night which showed significant coma on all four corners, with no appreciable tilt but severe curvature shown in CCDI (focusing using the thirds rule). Just as a test I took another image focusing right in the corner and the result was no different. The bahtinov pattern shows the same in focus display all over the frame. So my assumption in a previous post that getting a tilt free image and focusing nearer to the edge would improve matters, doesn't. If you have an image displaying tilt you can get coma free stars in two corners (and worse in the others) even if the tilt seems to be caused by the rotator after the rear elements. So I'm a bit confused. By its very design If the petzval elements aren't properly aligned you will get coma, but tilt and not focus can somehow change the coma effects. Eagerly waiting to see Es' Reid's analysis and whether he can achieve a fix. Alan

The 59.7mm distance quoted is so that the scope is focused at infinity when the focuser is fully back. I think there is possibly 1mm or a bit less spare so you can actually go through infinity focus. I made the spacing about 59mm so I had a bit more to play with. Using a smaller distance than recommended it will still focus at infinity but the focuser will need extending more. If using it for terrestrial photos this would increase your near focus distance but for astro use this isn't that important. I believe that to use a diagonal you have to remove the M56 to M48 adaptor to give you more distance to play with though an M56 diagonal is hard to find. I think WO will probably release one for use with this scope. Alan

The red RedCat dovetail was too small for the ADM saddle and I clamped an aluminium strip along side it to take up the slack. The white RedCat dovetail did just clamp firmly on its own. Maybe the gold paint is thicker than the red. Alan

Hi Nubian, I suppose you can only compare it with 250mm camera lenses so in that respect if you get one without tilt it would be significantly better. The image you indicated does show the tilt problem with the 'coma' like stars on the right. For the tests above I focused using the 'thirds' rule and with the last most flat image the stars in the centre still rate as the sharpest so it might be better to focus even closer to the edge than the thirds rule. I used the same focus point for each image so for those showing tilt, focusing closer to the area where the stars are at their worst would most likely give an improvement. The ASI1600 is a 4/3 size sensor (2x crop mode) compared to an APS-C sensor ( 1.6x crop mode) so the APS-C would show larger corner defects, though the colour sensor and pixel size may mitigate the effects to a degree. When the M48 to Canon adaptor arrives I can try it with my 700D camera. Alan

Here's the results from last night white RedCat tests. They are 15 sec L exposures on an ASI1600 given a levels stretch to make it clearer. I've shown the CCD Inspector 3D plot and a crop of the worst area and centre of each image (at full size). View images at full size for best comparison. The main problem is the camera rotator causes varying tilt depending on its angle. The previous Redcat had a more constant tilt while rotated. The first 4 images are with the rotator arrow at 0, 90, 180, 270 degrees with the last image being the best at around 300 degrees. As you can see the out of focus stars exhibit 'coma' like trails rather than just being a bit 'soft', even on the final image which doesn't look too bad in CCD Inspector. If the tilt can be eliminated it would be better and resampling to 50% or so which the images shown elsewhere seem to be, would give good results. Some might say I'm being too fussy I suppose. The red RedCat is with Es' Reid now. Hopefully he can fix the problem if it is just caused by tilt somewhere. Using a tilt corrector would improve matters, though it would mean leaving the rotator in one place and having to rotate the whole scope in its clamp which is fairly easy to do. I'll buy an M48 fitting tilt corrector from FLO and try it on the white RedCat. The M48 one just allows enough space to adjust it with the ASI1600 and filter wheel in place. The T2 tilt adjuster after an M48 to T2 adaptor doesn't allow room. Alan

Received the replacement white Redcat today from FLO, great service , and I'm afraid the first test image was not much different to the first scope with one bad corner. However rotating the camera orientation using the scopes rotator there was one point where the corner stars were better though still not sharp. At other rotation angles it was much worse with CCDI showing large tilt errors. I tried using a tilt adjuster to see if I could find a point where it could be cancelled out but it was too awkward. The camera had to be removed each time to adjust and you end up chasing your tail. The rotator was a lot looser to move than on the other scope so was wondering whether it was causing tilt when tightened. You have to focus on the 'thirds' and not the centre to get the flattest field, though it's still quite curved. I checked some photos on Astrobin using this scope and the full resolution ones are downsampled quite a bit and possibly cropped so it's hard to do a comparison. Maybe I'm expecting too much. I'll post some test samples tomorrow. Spent five hours and haven't got an image I liked. My WO-61 has much better corner stars. I'll wait to see the results others get and what the review by RayD says. If FLO send the returned scope to Es Reid for checking I'd be interested on what he finds. Hope I don't end up with egg on my face and caused FLO expense for nothing. Alan

I did that as mentioned in the paragraph you've quoted. The CCD Inspector results I posted above implies it's not the camera. FLO are delivering a new scope tomorrow. Alan

FLO have just received a delivery or white RedCats so offered to send one for delivery tomorrow at the same time as they collect the Red one for return. I was debating whether to wait for Es Reid to fix the bad one when you know you'll get a good scope back or get a new white one tomorrow. In the end I opted for a new white one as it's meant to be good weather for the rest of the week. Fingers crossed hoping it's a good one. Great service FLO as ever. Alan

Ooh! that's a bit worrying Dave. I wonder if FLO can send them to Es Reid for checking/fixing like the other WO scopes. Alan

Yes, that's correct Buzzard75. Alan

Thanks Dave, Clear Outside shows 5 green nights coming up so I thought I got the RC just in time. Alan

Yes it's a real pity Dave having waited so long. Now writing email to FLO. It's back to using the WO-61 then for the ASI1600. At least it's now much better once I got the tilt sorted out. Alan

You do agree it's a fault with the scope then Dave and needs returning. Alan

FLO. Have you tested yours from FLO yet Dave?

Took my first image with my new RedCat-51 this evening. Bahtinov focusing was very precise and easy. I used the ASI1600MM with filter wheel and took this 45 sec L sub centred on the Christmas Tree Cluster. Look at the bottom of frame particularly Bottom Left, out of focus smeary stars. I took three more subs rotating the camera through 90 deg each time and the horrible stars corners rotated 90 deg each time so looks like the fault is with the scope. I've included two CCD Inspector images of the 0 and 90 deg images which shows it clearly. I thought Petzval scopes were meant to save you having to bother with spacing and tilt troubles. Do you agree it has to go back? Alan

From the M48 thread the focus distance is 59.7mm. You can remove the adapter piece with the M48 thread to expose the M56 mounting thread. The focus distance from the M56 thread is 77.7mm. To remove the adapter, looking from the rear there are three grub screws in the centre of the 3 cutouts on the M48 adapter. Loosen these grub screws and the adapter unscrews. You will probably have to tighten the rotation lock screw first. WO only do three camera adapters from M48 for Canon, Nikon and Sony. I forgot to order the adapter with the scope and tried with an M48 to T2 adapter first but couldn't reach focus with my Canon. Have the M48-Canon adapter on back order. It may be easier for you to adapt from the M56 thread as there is more room to play with if you can find the right adapters. Alan

Vlaiv has pretty much said it all. If you look at the histogram curve of your image frame, (lights, flats, darks or bias), adding offset shifts the whole curve to the right, while reducing offset shifts it to the left. On the settings panel of some cameras 'offset' is labelled as 'brightness' but it's the same thing. Astrophotography processing generally involves stretching the dark areas of the images quite a lot and this is where the majority of the noise also occurs in the image. The darks and bias are used in calibration to help reduce the amount of noise present. If any frames have pixel values of zero it's highly likely that image data has been clipped, and then the calibration will not be applied correctly as the noise distribution in the frames is not representative of the true noise present. Adding a constant offset value to your frames avoids this situation happening. Like vlaiv I found the offset values often quoted for the ASI1600 are not high enough and you get some black level clipping. I've found an offset of 56 at unity gain just avoids this. It's worth mentioning that the ASI1600 (and possibly others) actually clip to a value of 1 and not 0, (well mine does anyway). This means that the minimum output value is 16 and not zero (when converted from 12 to 16 bit resolution). So values of 16 are most likely clipped values. At an offset of 56 the minimum value I get is 48 (16 bit) which is a value of 3 from the 12 bit A-D converter. So that's just OK. Alan

DHL delivered this from FLO yesterday. Was going to try it out during the day with the DSLR but being M48 rear it doesn't fit the standard T2 adaptor. In too much of a hurry ordering it to read the fine print. Tried with M48-T2 adapter but couldn't get focus. Ordered WO M48-Canon adaptor from FLO but they're currently out of stock. ? Will try with ASI1600 and filter wheel during the day as nothing to see at night at the moment. Alan

Hi pikecraig, at least it's not just me. I tried changing those same settings too to no avail. What processor/chipset is your PC. Is it a mini? As nobody else here seems to have the issue it doesn't seem to be a widespread problem. According to the tensforum link I posted Microsoft are aware of it and suggested disabling remote audio but that doesn't work for most. Consensus is that the March 12, 2019—KB4489899 update caused it. I just uninstalled that update and it hasn't cured it so hmmmm!. As you say hope there's a patch coming soon. Meanwhile just use 'Restore Down' instead of 'Minimize' and make it a little window in the corner of the desktop. Then 'Maximize' from there when needed. Alan

Thanks Sland, I've used Teamviewer and TightVNC in the past but they aren't as convenient to use full screen. Alan

Thanks SlimPaling but it would cost $98 to use on two remote computers. You're paying for 24hr tech support which isn't required for all of us just using a local network. I tried the video driver reinstall on the second PC but it hasn't fixed the problem on that one. Oh well, one out of two ain't bad. This has apparently been a problem reported with RDP going back to XP with a multitude of 'fixes' suggested, none of which are actual fixes as far as I can see. As it happened to me on 2 PCs around the same time as a Windows update I thought that might be the culprit. Alan

My only real preference for RDP is the easy full screen minimizing with a single mouse click. Full screen mode is necessary for multiple desktop working but other remote control applications seem to require multiple key presses to get in and out of full screen mode then a mouse click to minimize. I'm happy to be proved wrong though and if anyone knows of one that's as easy to use as RDP and doesn't cost a lot let me know. Alan

Device manager said the graphics driver was up to date. Went to Intel site and eventually found an Apollo Lake Celeron N3450 graphics driver. Installed it even though it reported it was older than the installed driver. No change on black screen. Went back to device manager to update driver back to latest which it did. However the black screen problem seems to have now gone away. I've had RDP minimized several times for durations up to 30 mins or so and it's been OK. It sometimes takes half a second on un-minimizing before the screen redraws but I'm OK with that. It's possible the latest windows update done a few days ago didn't update the graphics driver properly but forcing a re-install of the driver has fixed it. Hope so. Thanks Julian. I'll try it on the other Mini-PC tomorrow and see if it's 'cured' there too. Looked at dameware site and it's £290 for a single licence so I think I'll give that a miss at the moment. Alan

I've used both. Teamviewer is fine but needs internet connection to their website in order to save logon info. I prefer TightVNC because of this but both don't enable easy full screen working like RDP. You can't minimize full screen TightVNC without pressing Ctrl-Alt-Shift-F then minimize and vice versa. If they aren't true full screen you have scroll bars and I kept using the wrong menu bar as the remote one isn't in view. The only way is to use a smaller remote desktop but then the remote programs won't fit nicely. The choice of remote resolutions is too limited to find one that works. Hence I used RDP as my latest mini-PCs were Win 10 Pro. If anyone knows how to have 1920x1080 on local and remote with easy switching between them or easy remote full screen minimizing on TightVNC or Teamviewer let me know. I haven't heard of that. Does it resolve the issues I mentioned above? Alan The mini-PCs have standard onboard Intel HD Graphics. I'll see if there are any updates. Alan

In the past few days I've found that if you minimize a Windows Remote Desktop session and leave it minimized for around 30 secs or so when you restore it the remote screen is black. According to this tenforums topic it may be related to a recent Windows update. Suggested fixes don't work. I have two imaging mini PCs that I RDP into and this has occurred on both. They are both kept up to date which may not have been a good strategy. ? Does anyone else have this problem? I have Win 10 Pro 64 bit on all machines. The remote session is still active, it's just the screen doesn't get re-drawn anymore. To get around it I have to shut down and reopen the RDP session which is annoying. Alan