John

I've owned a few barlows and some Tele Vue Powermates. The Powermates are superb in my opinion. They just seem to be invisible in the optical train apart from amplifying the image. Your SN-10 is an F/4 I believe ?. F/4 is very challenging for eyepieces that have wider fields in respect of maintaining sharpness across the view. Tele Vue have made this a strength over the years. Be prepared to spend as much or more on eyepieces as you have on the scope though !

The TV plossls have really good transmission IMHO. I saw some data a while back resulting from throughput tests and the TV plossls were a bit better even than orthos (both classic and top tier HDs).

So you are both enjoying yourselves ?

I'm pretty sure that the TV plossl is a symmetric. I've seen the optical diagram on the TV patent and it sure looks like a symmetric. I've taken a few plossls apart over the years (not TV ones) and those have had what looked like 2 indentical doublet elements in them as well. Some of the older Vixen orthos also use the same design I was surprised to find, rather than the 1+3 abbe type ortho design that I had expected. I believe the feature that enabled Al Nagler to get a patent on his plossl was the curvature applied to the outer two lens surfaces which improved edge correction as I understand it. There is a rumour that Vixen NPL's use a similar design. On the 11mm TV plossl, I've owned a few over the years and found them sharp and contrasty. The eye relief is limited to around 75% of the focal length as it is with all plossls. The stiff rubber eyecup that TV use on the 11mm plossl can make accessing the full field of view a little tricky.

That is exactly what you need. You might need to try a "wanted" advert in our classifieds or on the UK Astro Buy & Sell website to see if anyone has one to spare.

I'd tend to go for a mirror at F/6.8. Thats what I use with my Vixen ED102SS F/6.5, Skywatcher ED120 F/7.5 and TV Ranger F/6.8. The Tak FC-100DL F/9 gets the Baader T2 Zeiss prism.

What matters is where the laser exits the objective. Don't worry about what it looks like when it hits the wall / floor / whatever. The tilt of the objective (stage 2 of the checks) is done with a cheshire collimating eyepiece, not a laser collimator. The last 2 photos posted by jock1958 show the the view through the cheshire collimating eyepiece when the objective tilt needs adjusting. You should see a single illiuminated disk rather than the 2 partially overlapped ones. Just to re-iterate, there are 2 stages which need to be carried out in sequence and 2 tools involved: 1. Check and adjust (if needed) the focuser alignment with the objective optical axis. This is done with a collimated laser collimator. 2. Check and adjust (if needed) the tilt of the objective lens. This is done with the cheshire collimating eyepiece. Where there are no collimation adjusting screws (very common), you can apply some tilt to the focuser by loosening the screws that hold it onto the scope tube and adding a shim or two to one side to tilt it slightly. Then tighten up the holding screws. If the objective tilt is out then things are more tricky but there are some tricks which can help.

I'll be going but I'm not sure of which day yet.

1. The scope comes with two 'adapters' that I need to put ion the scope before I can attach the eyepiece. Should I use both the adapters? This will increase the focal length and therefore magnification? Or better to just use one adapter then add the eyepiece? I definitely need to put one on, or the eyepiece wont fit.. I'm confused why there are two though. One adapter allows 1.25 inch eyepieces to be fitted, the other 2 inch eyepieces. You should use only one at a time. If you use both adapters, eyepieces will not come to focus. 2. It came with 25mm and 10mm eyepieces. Would you recommend a 5mm or barlow or something also? If so, which ones are a good choice? A 2x barlow lens is a good way to double up your eyepieces, the 25mm becoming 12.5mm in the barlow and the 10mm, a 5mm. The standard Skywatcher barlow (the deluxe achromatic one) is not bad quality for what it costs. A 6mm eyepiece is also a very useful focal length for the 200mm F/6 dobsonians - it gives 200x which is a bit more useful than the 240x that the barlowed 10mm eyepiece gives. 3. Is it really that important to get the scope to ambient outside temperature before use? I'm using it in my bedroom with the window open. Ideally it's best to use the scope outside and when it's cooled to outside temperature. Inside a house you will be viewing though heat thermals coming out of the window which can degrade the views at higher magnifications. 4. Can you recommend a good collimating device!? I use a simple cheshire eyepiece like this one: https://www.firstlightoptics.com/other-collimation-tools/astro-essentials-cheshire-collimating-eyepiece.html

The way that I do it is to remove the diagonal, put the laser collimator (which has itself been well collimated) in the drawtube and turn it on. At the other end of the scope, see where the laser beam exits the objective lens. If it is right in the center, the focuser optical axis is aligned with that of the objective, if the laser exits off centre, the focuser is tilted to some extent and it's opical axis is not aligned with that of the objective lens. I don't use the angled target face of the laser collimator at all for this test. To test the collimation of the laser collimator itself (which is importan as thay can often be out, especially with low cost units) I use this method: http://www.stark-labs.com/craig/llcc/llcc.html

Very interesting thread this, full of good tips and techniques to push as deep as you can go I can recall the evening when I managed, at long last, to see the Horsehead Nebula. I found it an incredibly challenging target and one that pushed my ability and that of my scope to the limit I think. I spent a long time that evening getting fully dark adapted. Our house lights were all off and the neighbours were all in bed. The sky was very dark and transparent, as good as it gets here. I "warmed up" by observing faint deep sky objects using the views that I was getting of those to guage whether the Horsehead was likely to be possible. I knew exactly where the Horsehead is located and had familliarised myself with the star patterns surrounding it so that I knew my way around without needing a star chart and knew how those star patterns looked through the eyepiece and how the area of sky looked with the H-Beta filter installed. I managed to avoid seeing an artifical light of any type for over an hour I think and by that time the reticule on my Rigel Quickfinder seemed glaring even at a low setting, so I switched that off. After all this the Horsehead Nebula was very, very subtle as I describe in my observing report. It's a weird way of spending a few hours isn't it ?. But, my goodness, its satisfying when it eventually comes together

I do have a TMB/LZOS 130mm F/9.2 triplet Alan - it's very close to the same weight and length as the ED150

I don't think you were imagining it either

I've yet to see the Alpine Valley rille in any of my scopes smaller than the 12 inch dob. Stu has done really well to get it in his 100 Tak As this is the eyepieces section I'll add that my favourite fine detail lunar observing eyepieces are the 5mm pentax XW with the 12 inch dob and my 3.5mm XW with the refractors.

My 12 inch F/5.3 Orion Optics dob weighs around the same as a Skywatcher solid tube 10 inch dob. I can move my 12 inch around in 2 parts pretty easily. It's almost a "grab and go" scope actually

The BST Starguiders are pretty good eyepieces and are generally better corrected in the outer parts of the field of view than Hyperions when used in a faster scopes such as your F/5 scope.

For a long time I eschewed scopes with apertures smaller than 100m because I simply found that they did not deliver views that were satisfying even if they were portable and quick to setup. Over the years I've owned a number of ST80 achromats, an ED80 and a William Optics 70mm ED doublet. A while back I picked up a used (quite old actually) Tele Vue Ranger 70mm and found that a really nice little package to use. It actually helped me out of a period when I lacked enthusisam for observing because it was simply so quick and simple to pop out and look through. The Ranger weighs just 1.6kg and I've got it on a photo tripod and Universal Astronomics Dwarf Star mount which together add 1.7 kg so the whole package is just a bit over 3kg - literally a one hand pick up job ! I've had some very enjoyable sessions with this scope since I've had it but I've not taken in travelling so far, despite its light weight and compact size. When I've travelled in the UK I've usually been able to squeeze a 100 / 102mm refractor and mount into the car and, so far, I've restricted myself to binoculars for trips that have involved air travel. The latter decision is mostly influenced by not wanting to inflict my hobby on my other half when we are on holday though - she gets enough of that when we are at home ! So I have now discovered the joys of a small and highly portable scope and where it fits into my hobby but travel has not really been the driver behind this as much as sheer convenience and the ability to have ad-hoc observing has. It might also be that my outlook on observing has changed in the past few years as well so that I appreciate what a small aperture scope can do rather than being frustrated by what it cannot

Stunning image !

My mum used to say that eating carrots would help night vision, or at least help you see in the dark. I suspect she was just trying to get my brother and I to eat up all our vegetables

I can only go my the experiences that I have had at the eyepiece because I've not had my max exit pupil measured or tried to measure it myself. Most (98%) of my observing is done from my back garden which suffers from some light pollution from major urban areas around 12-20 miles distant as well as locally produced LP. My low power eyepieces comprise the 21mm Ethos, 31mm Nagler and 40mm Aero ED. My largest aperture and fastest scope is my 12 inch F/5.3 dobsonian. With that scope, the 21mm Ethos delivers a 3.96mm exit pupil and the Nagler 31 and Aero ED 40 5.85mm and 7.55mm respectively. I consistently find that the 21mm Ethos provides the most contrasty views of faint DSO's, with and without a narrowband or line filter in use. I do use the 31mm Nagler and 40mm Aero ED from time to time to get a different perspective on the view but invariably find myself going back to the 21mm Ethos. So, to answer the question posed, for me and my usual observing location, 4mm is the most effective exit pupil. I'm nearly a decade older than Stu, which is probably relevant.

Great report on the big Panoptic I have the (by comparison, miniscule) Panoptic 24mm and enjoy it a lot. Most of my low power viewing with my 12 inch dob is done with my Ethos 21mm and, less often, with the Nagler 31. I find that the 21mm gives a darker background sky because I have a little light pollution here to contend with. Thats why I don't use a 40mm often so the Aero ED 40mm will do fine and I doubt that I could justfiy the additional cost of the 41mm Panoptic given the amount of use that it would get

Thats good news Doug and I'm very heartened by the overall response to this thread from SGL members

A 40mm plossl shows the same amount of sky as the 32mm plossl. The field stop in the eyepiece barrel limits the field diameter that can be seen and the internal diameter of the eyepiece barrel limits the maximum size of the field stop. Thats why a 2 inch format eyepiece can have a larger diameter field stop and shows a larger piece of the sky. To get a larger field of view than the 1.86 degrees that I've mentioned you will need either a 2 inch eyepiece or a scope with a shorter focal length. A 70mm 450mm focal length scope would show a 3.7 degree true field when used with a 1.25 inch 32mm plossl for example.

It depends on the eyepiece that you use. I assume that your 70mm / 900mm scope uses 1.25 inch fitting eyepieces ? A 32mm plossl will show pretty much the largest field of view that the 1.25 inch format can show and in your scope this equates to showing a true field of 1.86 degrees. This is around the same as 3.6 full moons. To work out the true field that you can see you divide the apparent field of view of the eyepiece (52 degrees in the case of the 32mm plossl) by the magnification that the eyepiece is giving in the scope, 28x in the case of your scope. So 52 degrees divided by 28 = 1.86 which is the size of the true field (amount of sky) that you can see. 2 inch format eyepieces can show larger fields of view but you have to have a scope that is 2 inch accessory compatible.

I know a reviewer who has contributed many times to leading astronomy magazines who told me just the same a few years back.