iantaylor2uk

I think if you put zero in the focal length box it will work out the right value for you

After weeks of cloud, we finally had a clear night in Chester yesterday. I managed around 45 mins on the Orion Nebula (30 second exposures, gain of 150 on ZWO 071 MC Pro camera, cooled to -5C) with my William Optics 81 GT IV telescope, with 1x flattener and UV/IR cut filter used. Stacking was in DSS, and some further processing was done in Nebulosity. I finally got a decent image of the "running man". This was also the first time I took flats using a light panel, and it seemed to work fine - just set Auto on the ASI Air Pro, and it came out around 50 ms exposure time.

Good luck with the weather. In my previous link to the YouTube video (higher up in the thread), the part of the video about the flattener obviously only applied to refractors, but the interesting part of the video (at around 6 mins) that discussed the effect of filters on back focus applies equally well to reflectors or refractors. If you insert a thin piece of flat glass into the optical path (of either a reflector or a refractor) it will push out the focus point slightly (due to refraction of light through the filter).

Welcome to the forum - I'm not too far away from you in Chester

Why don't you just a 2x Barlow on your shorter focal length scope? Would be a lot cheaper than a new scope.

Also worth adding you may need to increase your distance to the camera sensor slightly if you are using a filter. Typically, if the distance should be 55 mm, and the filter thickness is 1.8 mm, you should increase the distance to the sensor to 55.6 mm. A good explanation of why this is so can be found in this useful YouTube video: (the relevant discussion is at around 6 mins)

My advice would be to try it with and without the filter. The photos below were all taken by me last year with an f/4 12" Newtonian, and I did NOT use a UV/IR filter (and the camera was a ZWO 071 MC Pro which does not have a UV/IR filter in front of the sensor). These photos are not perfect as I did not use a Coma Corrector (I didn't have one at the time) and so have been cropped a bit. Hope this helps https://photos.app.goo.gl/zXxym5fbJ6JW6oKP6 https://photos.app.goo.gl/Jjpiu73ym3Wme7J57 https://photos.app.goo.gl/eDNKesm8ZSNoLCPX9 (there's some walking noise in this one unfortunately - although these were only 10 sec exposures)

You don't really need a UV/IR filter for a Newtonian unless you are also using a coma corrector. The optics in the coma corrector will likely mean you need one.

I find nebulosity pretty good for image processing after using DSS. There are some good tools in there (digital development + synthetic flat + auto colour balance) as well as the usual levels and curves.

I must admit I've never bothered with zero setting - on my WO 81 GT IV telescope there is a ruler inscribed, so I know roughly where the focus point is - I just leave the tube in that position so I know it is roughly focussed when the camera is on. When the ASI Air Pro does the auto-focus function, it then doesn't have to move very far in either direction. I think the zero function position is important if you start with the tube fully in or fully out so as to stop the motor trying to force the tube further out or further in.

There wouldn't have been a planet, or any atoms either, at the time of the big bang - the temperatures are so high it is thought there was just a quark-gluon plasma. When the temperatures cooled off, the first atoms/molecules to form would have been hydrogen - all other elements then formed from nuclear reactions in stars.

If you buy good quality equipment it will tend to keep its value (think of Takahashi or Rolex) or maybe even go up, if you ever need to sell. The most expensive thing I've bought is my mount - a Losmandy G11 - back in 2009 which cost around £2300, and since then I spent another £1000 to upgrade it to Gemini-2, but it should last another 20 years at least.

I've not looked through an Esprit, but can highly recommend the WO 81 GT IV. I use it with a Hotech SCA 1x flattener, so the focal length is around 478 mm, but you can always get the WO flattener/reducer if you want a wider field of view. Even at 478 mm focal length, when I use it with a ZWO 071 camera, the field of view is around 2.8 degrees by 1.9 degrees, which is big enough for most objects.

The G11 purchased new is pretty expensive in the UK but for some reason 2nd hand prices are fairly low (if they come up for sale). As new worms are quite cheap, and the electronics can be upgraded to the latest version, if you can pick up an older digital drive or Gemini 1 model for £1000 or less, they can be a bargain. I bought mine new in 2009 and it is still working well now with guiding RMS totals in the range 0.5-0.7" and it is capable of carrying up to 25 or 30 kg. I also like the Gemini goto system although recently I have been using the ASI Air Pro as you then don't need to bother doing any goto alignment routines.

I use a ZWO 2" UV/IR filter with my 071 MC Pro camera (you can get the filter here: https://www.firstlightoptics.com/uv-ir-filters/zwo-1-25inch-iruv-cut-filter.html) I recently imaged M33, although for only 2 hours, using high gain (240), 2 min subs with the sensor cooled to -5 C, and the photo can be seen on my blog: https://chesterastroblog.wordpress.com/2021/11/08/first-images-from-takahashi-tsa-102/ This was using a 102 mm f/8 refractor (with a 1x flattener). Some of the surrounding stars definitely had colour in them.

In my opinion it should work well in light polluted or very clear skies. In light polluted areas it will act as a light pollution filter, whilst also enhancing the contrast of the specific emission lines it lets through. In dark skies it will simply enhance the contrast of the emission lines it lets through. You would only use the filter on emission nebulae, there is no point using it on galaxies or globular clusters. Compared to a UV/IR filter, you need to take about 3x as long subs. Hope this helps

From the photos I've seen on the web, it looks to be the same focuser as on the GT 81. There is also a useful link here: https://digitalstars.wordpress.com/2019/11/08/how-to-install-a-zwo-eaf-on-the-william-optics-star71/

I've fitted one to a WO GT 81 and it works fine (I am using an ASI Air Pro, although the EAF is plugged into the USB hub on my 071 camera)

To be honest, I use an ASI Air Pro, with a ZWO 071 Pro camera, and each fits image is around 30 Mb, so if I take 30 sec subs for 4 hours that would be around 15 GB, and that is stored on a thumb drive, which you can easily transfer to a computer. You can always back the files up online if you are worried about hard drives failing although there may be a small monthly fee for that with Google or OneDrive.

I recently got a good second-hand Takahashi TSA 102, and have finally managed to get some images from it (it has been quite cloudy recently in the North-West of England, plus I had to order an extension tube before I could image - I got an SVBONY 90 mm extension tube which seems just about the right length). I used the Hotech 1x flattener, and a ZWO UV/IR filter, with a ZWO 071 MC Pro cooled camera. I used high gain on the camera (240), 2 minute exposures, and autoguided using the ASI Air Pro. The telescope is on a Losmandy G11 mount, and most of the time the total RMS guiding was between 0.5 and 0.7". I got about 2 hours on M33 and another 2 hours on the bubble nebula (I will need to try this last target again with my L-Enhance filter). Results look very promising for the first time out with this telescope. Note I had to focus manually because I need to work out how to attach the ZWO EAF to the focusser on the TSA 102. I also took a quick photo of the set-up on my phone which I've also attached.

If you use DSS for stacking, it rates the quality of each sub and you can tell DSS to stack the best 80% (or 70% or 90%, whatever you specify).

30-60 secs should be ok for most DSOs . You will still need to image for at least 1 or 2 hours (the more the better). There should be an optimum ISO for your camera that others could advise on, but I imagine you want the camera on ISO 800 or ISO 1600. You may not see much in a single sub but when you stack all of them and stretch/process the images, the DSO should come out. Below is an image I took recently with a one shot camera ZWO 071 of the North American nebula which a stack of 40 one minute subs with a WO 81 GT IV refractor (f5.9) with just a UV/IR filter. The focus was slightly off in the image.

I see from your signature that your scopes are quite fast at f4.8 and f4.9. Personally I would try 30 sec or 1 min exposures and just take lots of subs. You don't need to take multi-minute expsosures at those focal ratios, unless you are doing narrowband or using an L-enhance or L-extreme filter. What would also help is if you can somehow cool the sensor on your DSLR. I have the book "The Art of Astrophotography" by Ian Morison, and in that book he has a DIY icepack coolbox which may be useful.

Congratulations - I used to have an old Orion Optics DX300 (12" f/4 telescope) which I used on a G11 Losmandy mount. It was quite light, although in the case of that telescope it was because the tube was made of quite thin aluminium. If you're any good at woodwork you could make a radius block out of wood, it would be much cheaper than £450. Hope you enjoy the scope - when I first saw the moon through a 12" reflector I was taken aback how bright it was and how much detail you could see, so a 14" scope should be even better.

You can sometimes find second hand Orion Optics OMC140s coming up at a reasonable price, and these are usually pretty good optically, with a focal length of 2000 mm.