Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.



Advanced Members
  • Content Count

  • Joined

  • Last visited

Community Reputation

772 Excellent


About Tommohawk

  • Rank
    Sub Dwarf

Profile Information

  • Gender
    Not Telling
  • Location
    East Sussex
  1. Tommohawk

    Vignetting with reducer?

    Hmmmm. I think it's in my signature but I'm also on mobile and can't see! Anyhow its ZWO ASI1600 with 8posn fw. I've just looked at some flats from my previous setup - a 300mm camera lens - and the vignetting is similar. So maybe its the camera/filter combo. I'm using 31mm filters and that should be free of vignetting down to F4. Allegedly.
  2. Tommohawk

    Vignetting with reducer?

    I agree for testing the scope performance looking at star shapes is definitely important. But I'm still surprised at the amount of vignetting I'm getting. I agree this could be calibrated out, but I'm still surprised that its there in the first place. So - I'd be grateful for any advice on that specific point please- should I expect vignetting with this scope and reducer?
  3. Tommohawk

    Vignetting with reducer?

    Hi all Have just taken the plunge and bought a TS optics 72mm F6 Apo. First light tonight but hazy and really bright moon so not great time to test. I'm using a TS 0.79 reducer, and with Ha filters I'm getting pretty marked vignetting. Should I expect this? Ideally I'd be testing in LRGB but its so bright/hazy results are a bit poor. Any thoughts please?
  4. Tommohawk

    Sensor / reducer spacing question

    Couldn't agree more! And of course with the 31mm filters as you have to be careful not to muddle them especially the NB ones as they aren't marked and 2 of them are very similar in appearance- cant remember which. Telling which way round they go isn't easy either - the reflections thing sort of works on the NB ones, but it isn't obvious. If I were ZWO I'd ditch the 31mm filters and just offer 25mm or 36mm. I emailed FLO and they've kindly agreed to post me some masks - so that's one evening's entertainment sorted!
  5. Tommohawk

    Sensor / reducer spacing question

    Thanks Alan esp for the pic of the EFW. Cant remember the layout of the 8 posn one which I have - hopefully no overlap. Your masks seem to lie quite flat - are they plastic? I've emailed FLO - hopefully they'll have the masks, though the masks seem to be supplied with the EFW, not the filters, and I got the EFW elsewhere - cant remember where. You'd think if they get the masks FOC theyd be happy to oblige. I don't recall any of my filters, NB or BB, having blackened edges and I wonder if it might be easier to do that rather than fit the masks. Take your point about the safety bevel needing blacking and that's likely to be main issue I suspect. Either way its a horrible job and always heart in mouth re the screwdriver slipping. Also I wonder if the masks still leave you with 31mm clear aperture or does it reduce it a bit? Two of the new NB filters seem to have a different AR coating also, which makes it way easier to tell which way round they go if nothing else - I really struggled with this. My flat source is a bright monitor panel and I think this is what causes the uneven flats - which only occurs I think with the NB filters. Someone suggested using L flats for all, and this does seem to work OK. Initially I tried doing flats with Ha and that's where the problems arose - presumably because the filter transmits so little light that the bevelled uncoated edges transmit proportionately more compared to the L flats. If that makes sense! One big problem for me is that I only get to do AP occasionally - and in the big gaps between I forget all the idiosyncrasies of the equipment and processing techniques.
  6. Tommohawk

    Sensor / reducer spacing question

    Follow on - for anyone (probably me at some point in the future when I've forgotten) following this with similar filter issues, here is a thread on CN which deals with this quite well.
  7. Tommohawk

    Sensor / reducer spacing question

    Hi Alan and thanks for your post. First thing, I have solved the spacer issue I think ... in theory anyhow. ZWO supply with the ASI1600 a 21mm long M/F T2 extender, an 11mm long F/F T2 extender and a 16.5mm long F 48mm/M -T2 extender. So the combination of 21 and 16.5 would work nicely except that the F end is 48mm. But whilst having another firkle in my ZWO Box of Many Things, I found a 42 to 48 bush, so the F 48 becomes F42. Perfect solution! Well, I've got to acquire the reducer and scope yet, but it should be good.... and it must be a sign that I really should buy it. NOW what's all this about 31mm masks???? I bought my 31mm NB filter 23rd Jan 2018, and had some really unhappy issues with haloes and flats. I posted re this shortly after as I recall, but I didn't see any relevant posts, and assumes it was just me doing it wrong. The haloes aren't great, although I felt I could live with it - it was the flats that gave me real grief. I've just looked and as you say ZWO now supply masks with the FW. I guess ZWO, or maybe FLO (who supplied the filters) would probably supply masks on request. That said, it's a bit of a fiddle getting the filters in place, never mind with masks over the top - that must be a right whatsit! If they are thin, there's no way they would lay flat. Someone mentioned taping the edges I think to help them stay flat - but doing that must be horrible, and keeping the filters clean whilst ding it near impossible. Having followed a couple of threads on this, am I correct in supposing that the problem is with light entering the edge of the filter? I read that someone blacked the edges but not sure if this gave any benefit - that seems a better solution. Any thoughts Alan? One further thought - if light leaks through via the edges, you have to suppose it would affect the lights as well as the flats, no? Of course the source is typically more intense when doing the flats, but much shorter exposure. So same proportion, no? TBH I only got the 31mm filters because I'd hoped to image with something superfast, but if going with F5 or thereabouts I may as well have bought the 25mm version and saved some money!
  8. Tommohawk

    Sensor / reducer spacing question

    LOL - yes I've got quite a collection, none of which are ever correct for the job in hand!
  9. Tommohawk

    Sensor / reducer spacing question

    OK thanks that really helpful. These are 31m ZWO filters and I think only 2mm think. I assumed it would be measure from the main body but the I found the description ambiguous. Looks like yet another spacer than!!
  10. Tommohawk

    Sensor / reducer spacing question

    Quick follow on - if anyone could check my sums I'd be grateful! ♦ Focal Length to 350 mm .... 70 mm ♦ Focal Length to 420 mm .... 65 mm ♦ Focal Length 450-500 mm ... 61 mm ♦ Focal Length 510-600 mm ... 58 mm ♦ Focal Length 610-700 mm ... 57 mm ♦ Focal Length 710-790 mm ... 56 mm ♦ Focal Length from 800 mm .. 55 mm Scope has 432mm FL, so looks like I'll need approx. 64mm total spacing, increase to 64.5 to allow for filter increase in light path so 64.5mm FW is 20mm, sensor 6.5mm, so I'll need 38mm. ??? Agree?? also I have a 40mm adapter already - could I get away with this? thanks!!
  11. Hi folks - quick question please. I'm trying to sort the spacing from TS 0.79 reducer to sensor, using ZWO filter wheel and ASI1600. From the TS website it looks like I'll need 64mm spacing - but not sure which end of the T thread they mean when they say "Back Focus - distances from the T2-thread to the camera sensor" Do they mean the far end of the thread, or where it starts at the body of the reducer? Hope that makes sense! thanks Tom
  12. Hi Pete. Yes I really like the idea of a built in flattener not least because you know the spacing is good, but also the design ought to work better as its custom rather than an add on. Some folks seem to have had to really play around to get the spacings correct. If money were no object I'd definitely go for the faster TS Quad - the Imaging Star 71 F4.9 is 1299 Euros, which is a bit beyond my budget. This has full DSLR field, where I only need APS-c or similar for the ASI1600. Those comet pics are fabulous! And as you say the stars look great even with the camera lens. I've found the Tamron lens to be really excellent and fast as anything for camera work - but I find it too heavy for general photography so it doesn't really tick that box very well. I think I paid £300 for it so its a great performer for the price.
  13. That's a good observation! No, I took it in Spain so about 15 degrees higher than here. Still lowish though I suppose. That's where I'm off to in a few weeks, and hoping to do some more imaging from same location. Last time I has the DSLR running at >30deg C ambient! - this time I have the cooled ZWO, but I don't think I'll repeat the same target.
  14. Good points - for the money, youd expect the scope to outperform the equivalent cost camera lens. Nobody has commented specifically on the test pic I posted above. Maybe its unfair to ask, and I'm not expecting a guarantee, but - should I expect the Evostar DS PRO to do better?
  15. Hmm - not sure what happened there - I responded to this and it got lost - try again! Thanks for the input! Agree about the speed - camera lenses push it to the limit and it works fine for many things but not great for star shapes. To be fair though the shapes on the above posted image are pretty good I'd say. TBH that was probably done at F4 though. The Tamron lens has a 300mm FL, so a TS 72mm at F6 with a reducer will be similar and I can live with that. I came to the same conclusing re mosaics - I've done a couple of small mosaics and they work well if time consuming. One good thing about the Tamron is its solid as a rock, and build quality is excellent. By contrast I've read some comments about fracs from big suppliers having pinched and dodgy optics - that would definitely be a backward step. The other thing is that the Tamron connection to the ZWO camera and filter wheel is a breeze, where I've read that some fracs need a bizarre and unspecified collection of spacers to get the sensor distance correct and achieve focus - could do without that!

Important Information

By using this site, you agree to our Terms of Use.