John

A 4 inch achromat has to have a focal ratio of F/15 or so to show no false colour visually. At around F/10 the amount of false colour is really quite small so that is a popular focal ratio because the scope tube is manageable (ie: not too long). The achromats that operate at F/5 or F/6 do show quite a bit of false colour but their main intended use is for low to medium power viewing of deep sky objects and in this they do a good job.

There are filters that reduce the amount of false colour that is visible but they do tend to add a noticable tint to the image. Some people find them useful and some don't like them.

A 8 inch F/6 newtonian will show no false colour at all and is likely to show excellent planetary views.

If you use a 40mm 68 degree 2 inch eyepiece with the 115mm F/7.8 refractor you will get a 3 degree true field of view.

With a 6 inch F/5 the same eyepiece would create an  rather large exit pupil which would not be as effective IMHO so you would need to reduce the focal length of the eyepiece to something like 30mm. With a 30mm 82 degree eyepiece the 6 inch F/5 would show you a true field of 3.3 degrees so not a lot more than the 115mm F/7.8 can muster.

Depends whether you feel that the relatively small additional field and some additional light grasp is worth owning another scope for

1 hour ago, Mick H said:

👍

Telvue do a 32mm so instead of Focal reducer and 15mm the Telvue 32mm could be the way to go.

Expensive but hopefully I'll only buy it once.

The Tele Vue 32mm plossl is very nice quality but it does not have a wider field of view than any other 32mm eyepiece in the 1.25" format.

Just worth being aware of that.

47 minutes ago, Paz said:

I think I have this problem. I have almost a full set of Delos except for the 14mm which I didn't think I needed. But when a 14mm came up for sale recently I very nearly went for it just to avoid having a gap in a set. The thing that made me pause was that the end cap has changed design and I don't want an odd one out in my set. That's quite bad I know.

I've been there with the TV Naglers and the Plossls owning full sets of those for a while. But I also don't like to see an expensive piece of kit not getting used so that overcame the desire to hold on to full sets.

Incidently the 17.3 and 14mm Delos are not par-focal with the others in that range. For me thats good because it means that they fit nicely with my Pentax XW's and are close to par focal with them but I know that it does slightly annoy those who have full sets of Delos.

I said to my other half just a while back that I didn't think that I was OCD with my eyepieces these days. She gave me a funny look and said "Really ???"

29 minutes ago, JG777 said:

Some info here and @Ags had one.

 

Hmmm, maybe not then ?

If the original poster could do without slow motion controls the AZ-4 would do the job well as mikeDnight and paulastro have said.

Scope fettling - the ideal antidote to a rainy evening

If this weather keeps up, we will all have the best collimated, most highly polished and optically clean instruments anywhere on the planet !

Just been going though mine. Rather surprised to find:

8x21 unbranded

10x25 unbranded x 2 (pair in each of our cars)

8x30 Carl Zeiss Jenoptem x 2 (one old pair and one newer pair)

8x30 Swarovski Tirol

8x30 Komz

8x32 Opticron Adventurer Roof Prism

8x40 Helios Naturesport

10x50 Helios Naturesport

8x56 Opticron Vega II

11x70 Opticron Oregon LER

Where do they all come from - must breed in the cupboard

I find Polaris is a good star for star testing. Bright enough but not too bright. Easy to find (from where I am anyway) and it does not move (much) when being observed.

A green filter can be used to better discern the diffraction ring / airy disk pattern.

I agree. It's a good mount but the stock clamps are poor. They should have upgraded the clamps to a better design ages ago I reckon.

The reason why folks put up with that and upgrade the clamps is that there is not much that competes with the Skytee II in terms carrying capacity vs price.

For the 2 scopes that you are considering though, the 1st of the mounts that you posted links to should do the job. This UK supplier has something very similar on sale currently:

https://www.365astronomy.com/365Astronomy-AZ5-Versatile-Vari-angle-Micro-Motion-Alt-Azimuth-Telescope-Mount-with-Stainless-Steel-Tripod.html

I have a Feathertouch on my 130mm F/9.2 triplet refractor. It is superb in every respect. I like the Moonlites and have a couple of those but the Feathertouch is in a different league again. Pricewise too, unfortunately !

1 hour ago, grjsk said:

Hmm, that's a shame.  You don't happen to have any experience with any of these:

https://www.teleskop-express.de/shop/product_info.php/info/p8069_TS-Optics-Altazimuth-Mount-with-Fine-Adjustment-and-Quick-Release.html

 

https://www.teleskop-express.de/shop/product_info.php/info/p1753_TS-Optics-Altazimuth-Mount-GSAZ-with-fine-adjustment-and-tripod.html

 

The first seems to be the same as the VersaGo III/Twilight 1, and the last one the GSO Skyview. Both seems like a step up from Az-3/Az-5 in regards to stability, without a giant leap in price.

 

I have seen both above mounts and used the top one briefly but I've no long term experience with them.

From what I've seen I would agree that they are both a significant step up from the AZ-3 and probably the AZ-5 as well. I would be more attracted to the 1st one that you link to because of it's steel legged tripod. Heavier but a lot more stable than an aluminum tripod and it will resist the twist force that a longer tubed scope creates much better which = less vibrations and more stability.

The Skytee II mount is also available from that vendor and that is a very steady mount even with an ED120 F/7.5 on board. Another step up the ladder in terms of solidity and capacity. And cost of course:

https://www.teleskop-express.de/shop/product_info.php/info/p4537_TS-Optics-AZ5-Azimutale-Montierung-mit-Stativ-und-Feinverstellung.html

Once you have fitted the Moonlite to the Bresser, if you want to move it to another scope it's just a case of changing the flange. The rest of the CF2 focuser unit is standard.

It's not the weight so much but the length of the scopes that stresses the mount. The AZ-5 might be OK with the F/7. I have doubts as to how suitable it would be with the F/9 but it might be OK. The stock tripod of the AZ-5 is not too stable so a tripod upgrade should be strongly considered.

21 minutes ago, grjsk said:

Thanks for your swift reply. Do you think both of them will be okay on a simple AZ-3? I will most likely use a simple red dot and 1,25'' diagonal and eypieces, and not of the heavy premium kind. 

The F/9 will not be held steadily by an AZ-3. The F/7 would be pretty marginal as well I'm afraid especially if you try and use the sort of magnifications that these scopes are capable of.

An AZ-4 would be much better.

If the objectives are figured to a similar quality (which is likely) then there won't be a lot of difference, just a touch more false colour around bright objects and possibly the F/9 might be able to handle higher powers wiht a touch more aplomb. I have a 102mm ED doublet that works at F/6.5 which I think uses an FPL-51 element but the false colour is not intrusive at all.

A well figured F/7 ED doublet is a very versatile scope being able to handle both high powers and deliver wide fields of view at low powers 

I believe the TS 102mm ED (non-Photoline) uses an Ohara FPL-51 glass ED element. What type of glass the mating element uses is not defined.

The F/9 100 ED uses an Ohara FPL-53 element mated with a Schott glass element.

The levels of false colour visible in the F/9 are very low indeed from what I recall when I used to own one. The TS 102 that uses FPL-51 will be a lot better in terms of colour correction than an achromat of that aperture and focal ratio but is likely to show a little more false colour than the F/9 Skywatcher.

As Stu says, the F/7 will enable a wider field of view to be delivered and the focuser is likely to be better than the Skywatcher.

Depends on your priorities I suppose ?

A decent quality barlow lens, on average, reduces light transmission by 1-3%.

That is less than the variation in light transmission that is found across different eyepiece designs / brands without a barlow lens in play.

I use the Baader T2 Zeiss prism with my Takahashi FC-100DL and it works very well. I also have a couple of Tele Vue Everbrights and an Astro Physics Maxbright which I also think highly of. The Baader T2 suits the slim lines of the Tak very well but in all honesty I've yet to see any optical difference between it and the Tele Vue and Astro Phiysics mirror diagonals when I've swapped them about on my refractors

I have read BillP's reviews as well, more than once I have to say - they are good reads

These are all the flanges that Moonlite do for various refractors. My suspicion is that they won't have one currently with the Bresser AR127L name on it but one of the others is probably the right one, either a Meade or an ES probably because those brands have had strong connections with Bresser products. The question is which one precisely .....

https://focuser.com/refractorflange.php

If you can get the flange sorted out, the rest is easy

The Skytee II should handle an ED127 triplet OK if it is on a sturdier tripod than the stock 1.75 inch one. A 2 inch steel tube legged tripod or even better a Berlebach Uni should be investigated.

Even then you would probably have some vibrations to deal with at higher powers I reckon.

25 minutes ago, Paz said:

I am wondering if an apo around 100mm would better my st120/mc127 combination. 

I use my st120 mostly for white light solar with a wedge and solar continuum filter. Would the smaller apo do better in white light solar. In theory the extra aperture if the st120 would help it quite a lot.

Would a 100mm apo do better than my 127mm maksutov on doubles, lunar, etc. Again the extra aperture of the Mak is going to help it.

One 100mm apo costs more than my st120 and mc127 maksutov combined. I'd be interested in hearing any comments.

In my opinion a 100mm ED doublet would have the edge over an ST120 for white light solar observing with a wedge. I use my Lunt wedge with my Vixen 102mm ED and Tak FC 100 and the results are really good.

On double stars I think it would be a close run thing but personally I feel that good ED doublet refractors have provided the most satisfying views of double stars of any scope types that I have used. 

On lunar observing, again it would be a close run thing between a good ED 100mm doublet and a 127mm mak-cassegrain.

A quick "bump" for this heads up. More info on UK observation here:

https://www.popastro.com/main_spa1/transit-of-mercury-2019/

The trouble is that the GOTO function eats up a lot of a £350 budget leaving proportionaly less for the scope itself wheras without GOTO that budget would get you firmly into the 200mm aperture class.

It's a tricky decision I grant you.

Interesting thoughts Doug

Lots of clouds and rain do tend to prompt this sort of review. That, and lots of equipment tinkering !

The only thought that I have to offer currently is that refractors seem to get quite a lot larger and harder to mount steadily when they exceed 120mm in aperture. 

44 minutes ago, johnturley said:

I think its actually about 35 mm outward travel with a digital SLR (I must check with mine), were you meaning with an eyepiece.

John 

Yes, with an eyepiece. I've not actually used one though but I've read about the need for quite a lot of inwards focuser travel with this coma corrector frequently.