Eyepieces.. :(

[AweSIM]

hmmm.. nice.. i understand that now.. and hey.. i jus realized.. since ive got a 2" 2x barlow on my list instead of a 1.25" 2x barlow.. my budget has jumped up suddenly..

- TeleVue 2x 1.25" Barlow - 96 EUR

- TeleVue 2x 2" Barlow - 258 EUR

.... can i do with some cheaper 2" barlow? or not?

[AweSIM]

addendum.. please look at this item.. Crosshair Eyepiece 1.25" 12mm (69 EUR).. i was thinking of getting one of these at some point in time for alignment purposes.. has anyone used one of these? are these good enough?

[david o]

Hi again Asim,

This Revelation 2" ED 2x Barlow seems to have garnered a following here on the forum, it's essentially the same as this TS 2" ED 2x Barlow, but cheaper.

That cross-hair EP can be useful, but not essential to start with. Definitely belongs in the --[ Much Later ]-- category.

HTH

[AweSIM]

@david o.. thanks for the link my friend.. although im looking for a deal at telescop express.. your response has taught me a valuable thing.. 258 EUR isnt necessary.. ill look for a similar deal at telescop express.. thanks a lot.. ..

@everybody.. thank you everybody whos contributed to this thread.. this has been by far THE most informative thread for me.. from EPs to filters to focusers to the complete shopping lists.. EVERYTHING was covered.. and in so much detail thats baffled me.. and it has been so entertaining and interesting..

i thank the following people whove contributed to this thread and helped me make sense of things ive never seen myself.. (i dont own any scope right now).. ..

orion_the_hunter..

jamespels..

idlelimey..

tetenterre..

ronin..

adrian..

banner001..

jahmanson..

vicky..

special thanks to these people whove provided me with even more invaluable knowledge..

david o..

helen..

cuz of all you people.. ive learnt more in the course of three days than i wouldve in the course of three years and hundreds of wasted bucks thru trial and error.. i thank you all from the depths of my heart.. this really is a beautiful forum.. and you all are brothers.. ..

[AweSIM]

@david o.. again.. .. one final thing my friend..

i was going thru all the posts in this thread and i was wondering on your idea to get a DOB instead of an OTA only..

Hi again Asim

Just had a thought on the theme of Dobs.

Almost everyone on SGL that gets one comments on how easy and intuitive they are to use - it seems to become second nature in moments.

You could always have the best of both worlds ! Thus :

--[ This month ]--

- Buy a GSO 8" f/6 Dob, not the Explorer 200P DS Optical Tube Assembly, and so be able to do visual astronomy straight away.

--[ Within Next Two Months ]--

- Buy the EQ6, as planned, but with a set of tube rings and a dovetail plate to mount the Dob's OTA

Whilst the GSO Dob does come with a dual speed Crayford focuser there are some downsides. With its 1200mm focal length and f/6 focal ratio it isn't as suitable for imaging as the 200P DS at 1000mm & f/5.

Also at 449 EUR it's over one hundred €uros more expensive than the 200P DS too ! Not forgeting to add the cost of the tube rings and dovetail.

It is just an idea though. I prefer my Eq mount over my Alt/Az too

have a look at these two models..

SkyWatcher Explorer 200P DS

SkyWatcher SkyLiner 8" FlexTube Dobsonian

if i were to buy this DOB instead of the OTA only.. itll cost me more but like you said id be able to begin observations without waiting for the mount.. but my questions.. like always.. ..

1. you recommended GSO 8".. how does this compare to that one?

2. the focusers on these two scopes look very different to each other.. what gives? they're both CrayFord and i think the DOB one isnt DualSpeed.. although the DOB focuser looks better.. ..

3. the DOB is retractable.. and since the retraction mechanism isnt flush with the OTA body, does it mean ill face problems fixing it with tube rings and dovetail bar and mounting it on NEQ6?

4. the DOB is f6.. the 200PDS was f5.. how big is this a difference? ive been told that f6 is slow and not suitable for DSO imaging.. but i cant say since i dont know anything about these two scopes..

thanks.. ..

asim sohail..

[John]

I can have a go at your questions:

1. you recommended GSO 8".. how does this compare to that one?

GSO and Skywatcher optics are pretty much the same quality. Mechanically there is not much to pick between them either. GSO make the Meade Lightbridge dobsonians as well.

2. the focusers on these two scopes look very different to each other.. what gives? they're both CrayFord and i think the DOB one isnt DualSpeed.. although the DOB focuser looks better.. ..

With a fast scope (eg: F/6, F/5 etc) dual speed is useful as it enable more precise focusing.

3. the DOB is retractable.. and since the retraction mechanism isnt flush with the OTA body, does it mean ill face problems fixing it with tube rings and dovetail bar and mounting it on NEQ6?

Yes I think it would cause issues - truss / strut tube scopes are not easy to fit to equatorial mounts at all. Solid tube ones are easy however - you just need the tube rings and dovetail bar as you have identified.

4. the DOB is f6.. the 200PDS was f5.. how big is this a difference? ive been told that f6 is slow and not suitable for DSO imaging.. but i cant say since i dont know anything about these two scopes..

I'm not an imager but an F/6 scope should have a slightly smaller secondary obstruction and will be a little easier to collimate and keep in collimation. F/6 is not really a "slow" scope - in my opinion F/10 is slow. Perhaps "medium-fast" would be a better description of an F/6 !.

[AweSIM]

@jahmanson.. brother thanks for the response.. thanks a lot.. .. well the thing is that throughout this thread.. ive been told the importance of DS focuser.. so much that although i dont know anything about the DS (before i see it myself first..).. i am going to go for 200PDS instead of 200P.. if the SkyLiner DOB isnt DS.. then thats out of the question.. .. also for the reason you pointed out that SkyLiner may have problems fitting on NEQ6.. damn.. the scope looked good.. and is retractable.. .. .. .. ..

although the DOB david o suggested had DS focuser.. its almost 100 EUR heavier than 200PDS.. plus the fact that its 1200mm fl instead of 1000mm.. and although i havent got the experience to say if this is ok or bad.. i think i shouldnt go with something you more experienced folks are recommending against.. plus.. GSO DOB is plain white.. 200PDS and Skyliner DOB look cool too.. .. hehe.. i guess at my expertise level.. looks can be important too.. ..

[John]

All scopes look the same colour in the dark

[AweSIM]

very well said.. .. indeed.. but the cool colors are more easily justifiable to family members for the immense cost of the equipment stargazing forces you to pay for.. .. to them.. a tripod is a tripod.. you can get one at the hardware shop.. 1000 EUR for that is INSANE.. .. my dad offered me his camera tripod in an effort to reduce my budget..

[david o]

Hi again Asim

I think John has pretty much nailed it.

Couple of things to add from my (very limited) understanding of imaging :

An f/5 'scope will put more light on the imaging sensor than an f/6 'scope in the same length of time... a good thing.

The longer the focal length of the 'scope, the more difficult accurate tracking... a bad thing.

So for imaging the 200P DS is "better", a lower/faster focal ratio and a shorter focal length. Conversely, it'll be harder to collimate accurately and will be more demanding of any EPs you buy.

As always in star-gazing it's all trade-offs and compromises.

Hope this helps, at least a little

[AweSIM]

hi david.. it does help.. especially at my knowledge level.. everything you guys say helps.. thanks a lot ..

[david o]

You're welcome, Asim.

No problem

[AweSIM]

im so flooding with questions.. .. pardon me for that..

i just came across this item..

Complete eyepiece + accessory kit in aluminium case - by TS - 133 EUR..

this kit contains the following..

- TS Optics Super-Plössl EPs.. 32mm, 9mm, 6mm..

- TS Optics 15mm Wide Angle EP..

- TS Optics 2x Barlow Lens..

- 5x Colour Filters..

- Neutral Moon Filter..

- TS Optics EP-Projection-Adaptor

- an aluminium carrying case..

since i have already chosen the following items on my list..

- TS ED Barlow lens 2x - 2" - ED Element - BIG BARLOW - 83 EUR

- Tele Vue Plössl 11mm - 1.25" - 50° field of view - 66 EUR..

im guessing all the items in the TS kit are 1.25" EPs and filters.. the barlow on my list is 2" to make use of the stock 28mm EP that comes with Explorer 200PDS.. my question is.. is the kit really cheap (and hence inferior) or are the items on my list too expensive (and overboard)?..

the TS kit provides the following magnifications..

- 32mm.. 31.25x and 62.50x..

- 15mm.. 66.67x and 133.33x..

- 9mm.. 111.11x and 222.22x..

- 6mm.. 166.67x and 333.33x..

- 28mm (2" stock).. 35.71x only..

my setup provides me the following..

- 28mm stock.. 35.71x and 71.43x..

- 11mm.. 90.91x and 181.82x..

which ones better? i think the TS setup gives more options even though it might be 1.25" and the barlow might not fit the 28mm stock EP and also that 28mm stock is comparable to 32mm TS EP and hence redundant.. but at that cost.. i dont have high hopes with quality of these EPs.. and since 200PDS is fast and hence demanding on EPs.. i think i have more to lose than gain from TS.. what do you guys think?

asim sohail..

[EDIT].. i know it sounds stupid.. especially considering that most of the thread has been focussing on the fact that its better to get a few good EPs instead of lots of cheap ones.. but i just wanted to make sure since the description of the TS kit states the EPs are super plossls..

[AweSIM]

important update..

i just started using stellarium again.. i had it in my laptop but this time i tried using its occulars plugin.. stored information regarding the SkyWatcher Explorer 200P DS OTA.. and about the following EPs..

- 55mm (50 degrees AFOV)..

- 28mm (stock, unknown AFOV)..

- 28mm (stock, barlowed 2x, unknown AFOV)..

- 11mm (50 degrees AFOV)..

- 11mm (barlowed 2x, 50 degrees AFOV)..

- 3.6mm (45 degrees AFOV)..

- 3.6mm (barlowed 2x, 45 degrees AFOV)..

and activated the plugin and tried simulating what sort of views i can expect to see with these occulars.. (since i dont own a scope for now).. the results..

1. the 55mm EP is a must.. i thought 18x is a very low magnification but it turns out that FOV at this mag is about 2.5 degrees.. it gives best framing for orion nebula, horsehead nebula, andromeda galaxy, and other large objects..

2. the stock 28mm EP frames most other DSOs pretty well..

3. the 3.6mm EP frames jupiter, saturn best.. but at 277x i think its closer to the upper limit of possible magnification.. and barlowed 2x i think 555x is unrealistic.. besides since 200PDS is a fast scope.. it isnt suitable for imaging planets i think..

i think i now understand why high power EPs arent that desirable.. in fact i was hoping that there were EPs with even longer focal lengths.. unfortunately 55mm TeleVue was the longest i found.. .. please tell me is my analysis above correct?

one other thing i wanna know.. using stellarium i got a rough idea what sort of views should i expect from EPs of different focal lengths.. but if i use dslr to image.. how would i know how big the image is going to be since there are no EPs involved? im confused.. ..

asim sohail..

[AweSIM]

addendum.. ive read that reducers tend to increase coma in fast newtonian scopes.. is this true and to how bad an extent? i was thinking if it would be wise to buy an item such as Focal reducer 0.5x - 2" filter thread to further reduce the focal length of the scope and widen its FOV to capture more sky..

asim sohail..

[Merlin66]

Asim,

based on my fifty years experience -KISS - Keep it Simple Sunshine.

You don't need a lot of "dangle dolly" stuff to get started. As you gain practise and experience with your scope you will begin to appreciate what is REALLY needed and what never comes out the box. I wouldn't think there is a strong secondhand market where you are, so if you buy stuff and never use it I'm not sure you can sell it to fund someother things you WILL need.

Re Solar - save your pennies and just but a sheet of Baader Solar film. It's 100% safe and relatively cheap.

You only need a few - three maybe, eyepieces. Forget the 2" stuff.

A cheshire colimator, maybe a Telrad or red spot finder. That's about it.

Just my 0.02euro

[bombassa]

Hi

I have no experience with the 200 pds but at least in theory a 55mm 50* eyepiece in this scope would give an exit pupil of 11 mm. In general terms exit pupil should be best between 0,5 and 7. This would limit you to an eyepiece with a focal lenght around 35.

So if you want a really large field of view you would have to look for widefield eyepieces. But thats more $$$

Hopefully more experienced users will correct me if I'm wrong.

Clear skies

[AweSIM]

@merlin66.. brother thanks for the advice regarding the solar film.. and no.. the second hand market isnt weak here.. its NON-EXISTENT.. .. two questions if i may.. .. why forget 2" EPs? i had planned getting a 1.25" 11mm EP and a 2" 2x barlow to use with both stock 28mm 2" and 1.25" 1mm EP.. isnt that ok? also.. why telrad or red spot finder? the OTA already comes with a finder scope.. isnt it the same thing? i may be wrong though.. if you could clarify a bit..

@bombassa.. thanks for that info pal.. you just reminded me of the formula for exit pupil.. f# / EP FL.. and yes youre right in pointing that out.. exit pupil of 11mm is way too much.. so yea i wont be able to use any EP longer than 35mm.. but this confuses me as to why it isnt possible to see very wide field views with any telescope.. consider this..

- two OTAs.. FL 1000mm and 2000mm.. both with aperture 200mm.. hence one is f/5 and the other is f/10.. one is fast and other is slow.. one is suitable for DSOs at wide FOV while the other is suitable for planets at narrow FOV..

- for 1000mm FL scope at f/5, longest EP for 7mm exit pupil is 35mm which gives 28.57x.. for the 2000mm FL scope at f/10, longest EP for 7mm exit pupil is 70mm which gives again 28.57x..

- if we consider a third scope.. 200mm FL.. 20mm aperture.. at f/10.. the longest EP for 7mm exit pupil is 70mm which gives 2.86x..

- hence the larger the aperture the narrower the maximum FOV becomes? regardless of FL and F#? so if i wanna do some wide field work.. id be better off with a smaller scope?

thanks again..

asim sohail..

pakistan..

[AweSIM]

also.. im still confused about how big or small the image on a dslr sensor would look.. since there is no EP involved.. what would be the FOV captured by the dslr chip? i need to brush up optics physics i studied in uni.. ..

[Deneb]

The 200P DS is a nice all round scope for imaging & observing, maybe it will be a bit bulky to handle in the beginning, but you get used to it. If you want to just image, for a beginner, you can't go wrong with imaging with an 80mm ed scope, no collimation, no long cool down times, less bulky & portable...

Nadeem.

[Merlin66]

The stock finders are pretty average, and a zero magnification type are easier to use.

The 2" barlow I'm sure will cost more than the 1.25" (and weigh more - balancing issues) - you only use a barlow to get higher magnification so generally you'd be using 1.25" eyepieces anyway.

Re Image size on the CCD chip - google CCDCalc this is a freeware calculator.

[AweSIM]

@merlin66.. thanks for the info.. and VERY useful link to the CCDCalc program dude.. very useful.. i just select my scope F#, aperture and camera model and it shows my how much of the image will i see.. even if this is half as accurate.. its still gives a very good idea.. .. thanks a lot..

asim sohail..

[ronin]

The image size on the chip depends on the subtended angle of the object and the focal length of the scope. Don't need optics, geometry is adaquate. Work in radians then convert to degrees, it's a lot easier (x57.29).

A decent sized newtonian is really a visual scope, as Deneb says if you want to go imaging consider the 80 ED options.

Been on an imaging course and the noticable thing was that there were no reflectors there. Just refractors. Also go look at camera lens. Are they reflectors or refractors?

[AweSIM]

@ronin.. brother.. you just helped me get a grasp on the geometry of optics i had studied long ago but had gotten it rusty.. thanks.. .. but on the other hand.. why is 80 ED more suitable to imaging? till now i understood that aperture is most important along with F# for imaging.. but why refractors? ive been told by other members of this forum including ollypenrice that refractors are more suitable to imaging cuz they retain their collimation well.. and present small cross section to wind.. etc.. plus its a matter of personal opinion too.. as for cameras.. ive seen some on the net which have a short reflector based objective too.. but most have lenses cuz i think lenses seal the optical assembly whereas mirrors dont.. and mirrors can easily be scratched and lenses can not.. i may be wrong cuz you guys obviously know a lot more than i.. so can you please help me understand? WHY ARE REFRACTORS MORE SUITABLE TO IMAGING IN YOUR OPINION.. if its a purely personal-taste-oriented choice.. or even a convenience-oriented one.. id stick to my plan to get an Explorer 200P.. but if its more of a scientific truth.. i might have to rethink my decision.. ..

asim sohail..

[NickK]

Building on Ronin's point- imaging and geometry.

Imaging is basically capturing an image which may have pixels representing few arcseconds across. This means that the mount needs to move accurately enough to keep the square of the sky on the pixel.

The longer the focal length, the smaller square of sky is and the harder it is to maintain it accurately enough not to blur.

Use your hand, make circle with your fingers and thumb. Hold it close to your eye and look at the monitor. This is short focal length. The image is easily kept centred and there's no real movement. Now stretch your circle to arms length whilst keeping the same distance from your head to the monitor. You'll notice is moves a little around as it's a lot harder to keep your hand in the correct position.

This is the same problem a mount has. The ED80 are usually shorter focal length (~500mm) and so it's both (a) easy to guide and so doesn't require a really accurate (expensive) mount and ( gives a big impressive image as many DSOs are actually quite large. The down side is that you'll lack detail.

Now running a longer 1000mm focal length is like keeping your hand circle stretched out. The mount needs to be very good to keep the image steady enough when tracking the object. Over 1000-1200mm and you're looking at very expensive mounts! You trade the width of field for detail but there's nothing stopping you from using multiple images in a mosaic.