tooth_dr

The new 2.5” field flattener doesnt fit the focuser 🤷‍♂️ 👎🏻👎🏻

I received my SharpStar 2.5" field flattener today, and plotted the figures on a graph, to see what backspacing I should start off trying with my 517mm focal length scope. The last plot point was hard to know where to plot. I went with 500 and then 450mm. Does it look about right to aim for somewhere about 103mm as a starting point?

Interesting, especially since I'm using a refractor!

It was cold, but not cold cold, probably around 0 deg. Plus I have a dew strap running always on the lens to remove dew. I've only tried one other camera, D800E, and the artefact wasnt visible on the same stars. However there were unexplained diffraction spikes on a couple of other bright stars and a strange pattern closely around the body of the star: see below. Today I received the 2.5" field flattener, and intend to try this out as an alternative to the 0.8x FR, which I think might be the issue here. This will help rule that out.

Something is amiss. I had a check there and its actually in all the subs from two different nights, 30s 120s and 300s subs. I’d expect to see this in other people’s 2600MC images though if it was microlensing? I haven’t come across that.

That’s a shame Peter. What’s the problem with it ?

I also couldn’t believe the size of the 2600MC when i opened the box last week. My only experience of ZWO was a 120 and a 290 🤣🤣

I think then that 300s at F4.4 was part of the issue here. I am going to try gain 0 next time I'm out (whenever that may be). Thanks Richard Adam.

Brilliant Martin! You are the winner 😂 Looking forward to your first images. Hopefully the forum will be a good source of information on settings etc and getting most from this new camera.

Does anyone have any idea what is causing these unusual spikes?

Thanks Richard, the stars are much larger than I expected in my first light, so am just trying to get to the bottom of that. I dont think it was focus because I rechecked it twice during the run. I've ordered the standard field flattener to see if it fair out better, perhaps it's just too much at F4.4. As for the Ha data - it was OK, but the moon was just too overpowering and too close.

Mine is shipped also and is scheduled for Monday delivery.

The APS-C sensor offers 50% bigger FOV than the CCD believe it or not.

Well, the upsurge of Sony CMOS sensors will see a lot of people shifting (IMHO of course). I will likely be selling my Atik 383L and QHY9 mono once I get the other cameras up and running

There will be a few KAF8300 mono cameras for sale soon, including a couple I own. Are these worth considering for sub £700 price?

Nice!

Not familiar with how these work, but cant you just turn those screws with a pair of pointy nose pliers?

Dont want to derail the thread, but yes I just used the same handheld SW motor that takes the 9v battery. I did find that the motor coupling could slip on the shaft, due to the way it relies on a friction grip with a rubber O ring. I added a grub screw to that, and it was solid. In fact I had two ED80s, with same kit, so Im pretty sure it wasnt a fluke.

I had 1.8kg on the focuser on my ED80, and I didnt really find any issues mechanically. I never really scrutinised the star shapes, but felt they were ok also. Perhaps your focuser could be tweaked a little?

Very impressive Steve @teoria_del_big_bang

Light coming into the bottom of the scope would be my suggestion. Do you have a laptop or light shining at the mirror end?

That’s fantastic! Helps put it all in perspective

Definitely not stating the obvious. I would but am in a slightly awkward position. When I bought the scope, I wasnt able to get a focal reducer or field flattener for the 94 scope from the same supplier. I emailed about it, but they dont list it on the product range, and said it would take weeks or months to get it so recommended that I purchase elsewhere. As the scope doesnt work without either I had to source it from another supplier. I believe I can still return the scope, but will be left with a £328 focal reducer that wont be easily sold on. I havent heard back from the focal reducer supplier, but they dont offer returns (14 days only) but they do offer a field flattener for this scope, that brings it to F5.5 also, but at a slightly shorter focal length than the esprit (517mm). If it is to be believed, the field flattener delivers 'tack sharp stars' across a 44mm imaging circle, so this is a viable option to minimise loses, provided I can get an exchange.

I started off doing it with a mono and a DSLR, but the colour was noisy. I ended up then going to two mono, used one for colour with filters and one for lum, or one for Oiii and one for Ha. This time, I'm hoping the OSC will make it easier to get that colour data, and even with a dual filter, it will still perform ok for NB.

I'd say the jury is out on this one at the minute.