russ.will

I've attached a jpeg of screen grabs from Stellarium. Sorry if it distorts the page, but I couldn't keep the writing clear otherwise. Drag it to you desktop and use a picture viewer if it makes it easier. The top and bottom are both 40mm, but you can see the difference in increased actual and apparent field of view of the 2" 68deg SWA, although magnification is unchanged - The image is the same size, but viewed through a bigger window. The middle one is a 1.25" 24mm 68deg SWA EP which as you can see, basically covers the same amountof sky as the 40mm Plossl, but does so in a much larger apparent FOV. The advantage of the 24mm is that it is doing so at a higher magnification, which darkens the background sky, thereby increasing contrast. I cannot think of a good reason to buy a 40mm 1.25" Plossl, if you can buy the 24mm SWA. I just sold one for about £50, for instance.

Correct. Stellarium (free download) has a better scope/ocular/reducer/barlow simulator, but you can't export the images as easily. i find it very handy for saving my tired brain the effort of working this stuff out. You just have to bear in mind that even that doesn't show the relative changes in image brightness/contrast etc. Russell

Before you worry about buying a reducer, check the actual specification of the 9.25 OTA. If I recall correctly, the 9.25 is the smallest in the range that can take a 2" visual back - it just happens to ship with a 1.25" item. By swapping to a 2" visual back, you will also require a 2" diagonal, but these aren't expensive if you keep an eye on the classifieds. The important thing is that you are then far less limited by your maximum apparent field of view (aFOV). Take a look at this: The smaller circle is the 40mm Plossl, with it's tiny aFOV 40deg image circle. The big circle is a 2" 38mm EP, that because it isn't restricted by a 1.25" barrel, can achieve a 70deg AFOV. The image is the same size (the magnification hasn't changed) but now you can see a lot more of the area you are looking at. Think of it like looking at the same view, from the same distance, but through a much larger window. Now look at the same pair of circles, but this time I've added the 0.63x Focal reducer to the 40mm Plossl: The reducer has allowed the Plossl to cover the same area (actual field of view) as the 2" EP. What this graphic doesn't show, is that because the aFOV is limited by the EP size, when you look in the EP, that blue circle and everything in it, will only look the same size as red circle. That's right; In case you haven't done it already, looking down a 40mm 1.25" plossl is a bit like looking down a toilet roll - It's all a bit light at the end of a tunnel Okay, you have to buy a 2" visual back and a 2" diagonal, but you only have to do this once. Being bigger, it will be stronger and more stable and as they always come with a 2-1.25" adaptor, all of your current 1.25" EPs (barlows, etc) and any you buy in the future, will still fit in it. Likewise, 2" EPs are more expensive, basically because they have larger lumps of glass in them. But make no mistake; when it comes to maximizing actual and apparent field of view in a long focal length scope, there is no substitute. Russell

With money in pocket, I went to view three 'scopes side-by-side at ENS Optical. ENS Optical have an eBay shop-front (their own webshop is currently being developed) but also a physical shop, where you can actually view what you're buying. For me, this is important, especially if you are considering scopes you have no experience of. Only a few minutes off the M6, NE of Birmingham, they're very central too. They're not (currently) a dealer of any new products and I don't think Steve (who is ENS) would mind me saying that when you enter the shop, it's a cornucopia of optical madness. If you're expecting only the items you see on the eBay Shop, you will be visually assaulted by the sheer weight and apparent confusion of a shop stuffed to the rafters with optical - including 35mm photographic - goodies. I should mention that in my yoof, I used to work in an establishment called The Cambridge Camera Exchange which had a photographic history running back to 1900. The stock profile was an eclectic mix of every single darned photographic camera or lens that spanned near 90 years and most of the staff tended to think a lot of it was only fit for the skip. If you walked in there thinking you knew photography, you didn't, but you walked out, blinking into the sunlight, years later with an understanding that couldn't be gained from a magazine, or as it would be today, the internet. What a few years of service gave you, was the ability to put your hand on a left handed iblescritch in the completely uncataloguable stock, the one and only time someone on earth asked you for one and for that reason, TV and film companies (we supplied Memphis Belle, to mention one) flocked there on a regular basis for chronologically correct photographic props. The reason I'm saying this, is because when I first walked in, Steve apologized for the mess, but to me, this was like putting on a comfy slipper. Everywhere I turned was something interesting (A 16" Sonotube Meade Dob was quite striking, but by no means the most unusual) that I couldn't resist picking up to look at and I loved it. I loved it, because this is a person steeped in the love of optics and not just the sales of it and that IS a difference these days. Each time I wanted a widget, Steve would ferret at least one out. In other words, ask! He's probably got one. I was arriving with prior notice, as I find this is the best way to get to see what you want, with any bricks and mortar dealer. Indeed, several of the emails exchanged were answered late in the evening, which is not something you can expect. As I turned into the car park all three of the scopes were parked outside ready for playing with. I had as much time as I wanted and was plied with multiple cups tea that would put hair on your back, never mind chest. Every question, stupid or otherwise was dealt with. You don't get a sales patter and honest opinions of the scopes relative strengths and weaknesses given. This is important, because second hand scopes tend to be more 'individual' than a brand new carbon copy. It's seriously helpful to have someone know about the sorts of issues that can be found through surfing, plus some that only ownership will reveal. All in all, a relaxed and very informative couple of hours with a very pleasant bloke and one I was happy to make a purchase with. Highly recommended. Russell

I considered running mine under the tap and then decided I couldn't be bothered to clean off the water stains that would result - Hard water area, you see? Baader Wonder Fluid rules! Russell