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First light for first refractor


spaceboy
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Hi All

Some may know that I have pondered the idea of a refractor for several months and finally I went with it and picked up a second hand Evostar 120. Unbelievably even though it was 2nd hand and may not count as "new kit" the sky's actually stayed clear for once so I was able to get in some 1st light observing :p

I have only ever had reflectors of one type or another so my first look through an achromatic refractor felt almost how I imagine it would feel for all those people back in the 1974 when the first colour images were broadcasted. WOW! colourful would be an understatement :). Don't get me wrong, but how anyone could say it isn't distracting must be pulling yer leg! I must admit it is quite a sight seeing Sirius in a halo of purple and Joseph's dream coat on Jupiter but I did actually enjoy the views. I am more of a DSO man myself so my choice of the 120 despite a well documented CA was always going to be my favored choice. On this count the 120 for me didn't disappoint and the view of M42 was well contrasted even against the early evening sky. It was also nice to be able to frame M45 perfectly which due to exit pupil fails to fit with in the view of both my reflectors. I have always had to settle for using my binoculars on this object and although an amazing view some details are lost due to the lack of magnification. The double cluster in Perseus was also good but I will say no where near as impressive as it was in my 127 MAK.

The refractor will certainly stay in my collection as I now have the best of both worlds but I think achromatic refractors should be sold with fringe killer filters as standard just to take the edge of the false colour as they are a nice scope to use and give some good views but some detail can be lost due the the full beam glow of a purple halos.

Even though getting the refractor I have always wanted I am still torn by the whole reflector vs refractor debate. For me CA aside I did really enjoy the wide views, contrast and sharp stars. What I didn't like was although you do see more sky it was like being a kid again and looking through an old polly roll tube up at the sky. I don't really notice the Field stop in my reflectors so for me I found this more so distracting than the CA.

I now know why the refector, refractor debate has never been resolved.

SPACEBOY

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Iis weird - I dont see much CA in my TAL except on super bright objects and even then its very well muted. A pale yellow filter usually knocks the CA out.

Maybe the extra two stops of F number makes a big difference the TAL is almost F10 versus F8 - I dont know.

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Interesting write up - thanks for posting it :)

I've owned an Evostar 120 and a couple of Evostar 150's and didn't find the CA too bad - and up to then I'd only owned ED refractors. It is the F/8.3 model you have isn't it ?.

As you say though, perhaps it's more noticeable to some than others, like astigmatism in eyepieces.

Does yours have the collimatable objective lens cell ? - I guess it's possible that the collimation could be off kilter a bit and adding to the CA ?

Edited by John
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It is the older 120 blue tube with a collimatable lens. I was aware there was some issues with QC on some of the older models so I may well have got myself a lemon ready for shrove Tuesday :p Collimation was why Sirius was amongst my first light objects and it was smack on both sides of focus. It may well be that I am so used to my views through the reflectors that had me in ore of such a palette of colour or I managed to find the one scope that made it through QC unchecked. I don't suppose a scope that's not cooled down properly would show worse than usual ( what ever usual is??) CA?? I should have guessed really as the scope is 24 months old and mint almost to the point it hasn't seen much use. Wonder why that is :)

Don't get me wrong I am more than happy with the scope on DSO's but I will be looking out for fringe killer filter for brighter objects. I was aware after all the advice given that achromatics suffered some false colour but never having had any experience of CA or refractors it came as a bit of a surprise. Guess I am just stuck in my ways having only used reflectors. If I could afford a 120 Apochromatic I would have no hesitation in buying one as I am finding a refractor has a certain charm about it and the views are superb for some thing that is several inches short of what I am used to using.

As mentioned, the only down sides I felt personally and although nothing I couldn't get used to is the some what feel of a port hole view despite offering a large view of the sky. Another thing I noticed is that due to where the EP is situated it can be a bit fiddly on an EQ mount to reach the RA/DEC knobs while still keeping an eye on the sky. I remember when I first looked in to refractors John recommended AZ mounts for fraks and I now see the advantages of this. Another easy but expensive fix would be to get motors for the EQ5. Other than the above and for me the obvious CA ( but I may have one of the poorer examples ) I can understand why so many people have refractors and mine will be staying for some time to come.

SPACEBOY

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You might find the CA (and the views generally) do get better when it's cooled for around 40-60 mins. I know refractors are not supposed to need so much time to cool but I find my 4" ED and 6" achro certainly do need that time and the views benefit from it.

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I admit in my eagerness I didn't hang around getting outside and in the EP. Thinking about it, it would make sense given the purple halo looking some what like frosted glass. I never gave it a thought to checking if the lens had steamed up. TBH I only wanted to give it a quick once over and check collimation so I may have been a little hasty with my first light report. I will give it another go once I get chance and make sure I get it cooled down and update my review. Saying this I have some uncanny bad luck so it dose stand a good chance I got the bad egg but I will remain optimistic until my next observation session :)

SPACEBOY

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I agree with John on the cool down time. I normally leave My Tal 100RS out for about 30 minutes before hand and it does make a difference. False colour is really minimal with the Tal anyhow but i think the 30 minute spell leaves the whole views just that little bit sharper.

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I agree Damo636. I still haven't had chance to go out and check but I have my fingers crossed that it was just the lack of a suitable cool down. I had a similar thing happen with my 15x70's and they are no where near the size of the Evostar. Having never looked through an achromatic (other than binoculars) I don't really know what is acceptable but I will probably get a fringe killer filter either way.

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2ND LIGHT UPDATE:

I managed to get out for and hr or so with the Evo 120 last night and put it to the test again. The scope had been stored in a cool area so I was hoping this was going to reduce the cool down time needed. Needless to say the first object on the agenda was the moon. As with my first light report I was using my TAL Plossl EP's again which TBH could do with a lens clean, and for the moon a TAL moon filter. Ever eager I was straight in the EP again. I wasn't expecting miracles as it had now only been outside for 10 minutes so as suggested by you guys some cooling would still be needed. Over to the moon it was and I have to say a sigh of relief came over me as this had to be the most amazing view of the moon I have ever seen. There was no false colour that I could make out other than a VERY thin blueish/purple line on the very edge of the moon. To be fair it had to be looked for and was not in the slightest distracting or even noticeable at times. What I did notice was a great deal more contrast to the surface showing a dark patch I had never really noticed before. For the most of the time the image stayed really sharp even though I later confirmed with my 200p that the seeing was back to it's usual turbulent self. The 200p was a more washed out view of the lunar surface and effort was require to make out the darker patch that the Evo made so apparent. It also struggled with the magnification and never really offered the sharpness of the Evo.

Although the moon was high and very bright I panned the Evo over to M42 for another quick look. I could make out a fair bit of detail but the view was lacking any real contrast to the back ground due to the moon sitting not far above. I did how confirm that even though the scope was cooler that the trapezium stars still looked yellowish but not as badly as the first time. Next was the one I knew was really going to see if cool down made a difference, Sirius. At 38.46x (26mm)I was thinking yeah as there was no real distraction but then I realized the first attempt was at 158.3x. I swapped over to the 6.3mm ep and again the halo was in all it's glory beaming like those static balls you get in gadget shops. I would say that it was no where near as bad as the first time but still in no way appealing to look at for any length of time. A quick star test did suggest the collimation may be out a little but I put this down to bad seeing as I doubt the collimation could have been lost since my first light report. I'm not usually a moon person but I kept on coming back to have another look. I really enjoyed the experience and for me it was like that first time looking at the moon again. That thrill of seeing with your own eyes all the craters and mountains :o Anyway dragging myself from the moon I had another look at M45 this time seeing how much magnification in to it before it lost it's frame in the sky. The view of M45 alone makes the Evo a keeper for me as I just can't get all of M45 in to view with either of my reflectors but with the Evo it is possible to frame it and then some. A disappointment was going to come as I thought I'd see how the Evo performed on the Algieba double in Leo. Again flaring was at times so colourful that it made it all too distracting a target. This was a target that I later compared in the 200p and although the seeing proved to be the reason for difficulties splitting the double the white light glare from the two stars was less of a distraction in the reflector and I could comfortably wait for flighting moments when the doubles split cleanly.

My review is based on my personnel opinion and although there is question about the quality control of mass produced budget achromatics, I can't say whether the experience would be all that much different in another Evo 120. I can say that a dramatic improvement was seen between my first and second light experience simply due to a more ambiently cooled scope. The views of the moon are by far the best I have ever had and I no longer feel the need to curse at the skies when the moons out. I think and hope I will see even more of an improvement when I am able to use better EP's in the scope but at the moment this is a no go due to thumb screws. I think pleiades will really pop when I push that little bit more magnification in to it while keeping the FOV. Overall it is an enjoyable experience to use a refractor (as long as the tripod is fully extended) and there is no doubt that the views are more steady than with an open tube and for this reason it may offer more observing opportunities. It is debatable whether I would be so happy with it if I had purchased at new prices as I think the money would be better spent on a reflector. In this case the EVO 120 retails at the same price as an Explorer 200p and both sit on an EQ5 mount comfortably enough for visual so for the same outlay for me it would be a no brainier. I can certainly see the appeal of the Apochromatic refractors if they offer colour free sharp contrasted views and if my numbers ever come up I would have no hesitation in investing in a 120ED as even my budget scope has offered some amazing views on selected objects. What I did like most about the Evo was it was a doddle to set up and was so easy to handle up and down stairs. The OTA comes in at 5.9kg which is similar in weight to the larger 200p but is not as cumbersome to handle. At the end of the day it is what it is and it dose what it dose. It is know to most astronomers that you cannot get a swiss army telescope and this is why most of us have more than one. I am still happy with my decision to go with the larger 120 despite it being said to largely emphasize CA over the smaller 102. Investment in a filter will be required to compensate for this decision on brighter objects but I feel it will be a small price to pay for the extra bit of light grabbing aperture.

Out of curiosity, if the collimation was ever knocked out how do you collimate refractors? The scope came with a cheap Cheshire type collimator but I have never used one. I take it laser collimator's are no use? And what would the recommendations be for a CA reducing filter?

SPACEBOY

Edited by spaceboy
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I'm glad that the refractor is starting to perform for you now :o

I use the approach set out here to collimate my refractors (using a collimator identical to the one pictured) and it works well:

Refractor Collimation

Once the scope is fully cooled (60 mins I'd say) and with decent observing conditions you should get an infocus star image like the ones pictured at 150x or more - a single diffraction ring at focus is normal.

Your scope should split Algieba cleanly at 120x or more.

There was a thread on SGL very recently about CA filters:

http://stargazerslounge.com/equipment-discussion/133909-best-ca-removing-filter.html

Not sure it reached any particular conclusions though. At F/8.3 the CA with your scope should be reasonably well controlled - the view you describe of the lunar limb sounds about right.

The most effective device to control CA that I've ever used is an Aries Cromacor corrector which I use with my 6" F/8 Meade achromat at the moment - these are out of production now and rarely found unfortunately :(

Edited by John
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Interesting report Spaceboy, thank you.

I would also like to hear how the Evo performs on Saturn, could you let us know??

Thanks Steve

Will do Steve. I did want to give it a go last night but I have been having problems with the GT mount on my main scope so I needed to get that sorted and while there do a reflector comparison to what I'd seen in the refractor.

I'm glad that the refractor is starting to perform for you now :o

I use the approach set out here to collimate my refractors (using a collimator identical to the one pictured) and it works well:

Refractor Collimation

Once the scope is fully cooled (60 mins I'd say) and with decent observing conditions you should get an infocus star image like the ones pictured at 150x or more - a single diffraction ring at focus is normal.

Your scope should split Algieba cleanly at 120x or more.

There was a thread on SGL very recently about CA filters:

http://stargazerslounge.com/equipment-discussion/133909-best-ca-removing-filter.html

Not sure it reached any particular conclusions though. At F/8.3 the CA with your scope should be reasonably well controlled - the view you describe of the lunar limb sounds about right.

Thanks for the info John. It is amazing how much better the refractor was cooled down. The problem having an observatory scope is that I forget how long scopes have to cool. I had seen the link you sent about filters and the follow up but TBH I am some what confused by it all. The views I had of the moon last night looked the same as the bottom picture http://stargazerslounge.com/equipment-reviews/67599-baader-ca-filter-comparison.html Semi apo filter. I can honestly say there is no problem viewing the moon and is in fact far better than my 200p. The issue is with the bright stars and possibly planets but I will have to hold off my verdict on Jupiter as my first attempt was with a warm scope and a low on the horizon Jupiter which wouldn't be the best anyway. My point is if I already get the same view as the semi apo filter shows in the review would it actually make any difference in my scope to get one? The problem is I don't have a clue what is acceptable CA and what is excessive. Look through the Evo at the moon and then at a bright star and you would think you are looking through two different scopes. I would like to get a filter to help with the CA but even the cheapest of filters cost more than what I paid for the scope so it doesn't make sense to go spending too much money.

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Come on Kef9 you don't need to suffer poor CA through that ST150. Join us on the dark side and get yourself a nice 150p on a EQ mount. Splash the cash my friend and while your at it I will help out with the funds by taking that Semi-apo filter off ya :hello2::hello2:

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LOL!!

I dont mind the CA actually. I think its affects are overated and I use the ST for DSO's anyway. For planets I switch to the C100ED which takes about 30 seconds.

I just love the grab and go nature of refractors. No messing.

You really want the semi apo :D I haven't used it much yet really but if I sell you will be the first to know.

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You really want the semi apo :p I haven't used it much yet really but if I sell you will be the first to know.

Cheers Kef9 I'll keep you to that :D

Yes I think a SA filter will be my best bet. I just can't get on with the CA the refractor gives but I enjoy the refractor (if that makes any sense). I'm sure I will get used to the inherent flaws of an achromatic but I now know why everyone recommended a 100ED. One did come up the same time as the Evo but as there was mention of filters that would help with CA the Evo was a deal to good to be missed. Little did I know these filters come with there own flaws (yellow hues) and the ones that don't are rare on the second hand market in the UK. I did see a SA on CN forum but I take it they have a 50 post rule also?

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Having given the lens a clean I'm now left with residues from lens fluid on the lens but the purple halo around Sirius has reduced and the double in Leo split cleanly. My problem now is I have been bitten by the refractor bug. If only I'd jumped on that C100ED when I had the chance. The views in the Evo have definitely improved from a clean and longer cool down but I can't help but think how much better an Apo or Fluorite would be. I'm thinking it would be nice to have a refractor that is good on the planets as well as the moon. The evo brings out so much contrast on the moon compared to the 200p but I have read the false colour of achromatic makes them not so good on the planets. I no longer see the point in getting a filter when the money could go towards a better corrected frak.

I take it the best budget scope would be the C100ED as previously recommended in another thread?? But are there any others to look out for??

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Are they R&P the C100 & ED100?

I have just tweaked the R&P on the Evo. It's silky smooth with no slop. Some back lash there but I can't see how it would be possible to get rid of that? Compared to how it was originally it's a vast improvement but a crayford it's not. In the end I couldn't justify chasing the expense of a crayford on the Evo when considered it doesn't actually improve the image in any way but I would assume they are a must have on semi-apo's.

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The stock focusser in the C100ED is very poor. Optically they are superb but I will look to upgrade the focusser in the future when I can be bothered.

The scope though is the baragin of the century. Im so glad I got mine! :D

Edited by Kef9
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I did have the chance of getting a C100ED but an Evo came up at the same time for practically nothing and as I wasn't sure if I'd like refractors this seemed the obvious choice. I was a bit dubious about refractors as you look through the lens as apposed to a reflection. The improvement in image quality from a quick clean proves the design can have it's short comings. But it is shocking how much more contrast they offer over the reflector. (on the moon anyway) I may try stepping down the aperture next time I use the flek on the moon just to see if it's the larger aperture that is washing away the contrast.

I would give some thought to adjusting the R&P on your ED as the difference is huge in comparison. I used some mouse Teflon tape (£2 off eBay ) with some double sided foam tape and some lithium grease on the rack. I'm sure with more tweaking I could get it to turn Even more freely but my main qualm was the sloppiness which has now gone. You'll never beat a crayford but is it worth it on a colourful achromatic?? I did almost buy a crayford but the sale fell through. Kind of happy it did now as I'd rather put the money towards a better scope.

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I think the focusser upgrade is worth it. At the end of the day you can take it off and attach it to the new scope if its a synta. I plan to get a crayford (or moonlite if I get silly) but it will see use on both of my scopes as I can interchange them.

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  • 4 weeks later...
You haven't seen CA until you look at Sirius through a ST150!!! :)

It will do though until a 6 inch triplet apo comes along in about 10 years!!!

Ok, mine is 133mm oil-spaced, 4-element, f/12 Apo, not 150mm - but it is a killer scope. The Apomax was made in 1996 (only 23 of 'em), the same fellow reportedly made three 200mm scopes of the same design. I actually saw one of them - it was an awesome site to behold. Sadly, this was in the day time and I never had the chance to look at it in the dark! :)

Scopeboy,

Sorry about your CA problems. I think if you stay away from Sirius at 165x, you will do pretty well! If you really want some fun, try splitting some doubles with that thing. It will really outperform your reflector on that sort of task, globular clusters are also a brilliant target for it. Double star hunting is somewhat out of fashion, but I find it really enjoyable... with the right kit, of course! :(

Dan

Edited by Ad Astra
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