M42 as never before.

[ollypenrice]

Once both imaging setups were whirring away I put the new 26mm Nagler in the 20 inch for a first light of the EP. M42 was still around so off we went.

The big Dob always has some astigmatism (maybe the secopndary) and it was more of a problem to get your eye right in the Nagler than in the Panoptic 35 but once you had yourself comfortable... incredible!

With a too-big-by-far exit pupil the Pan was squandering light. In the Nagler it went straight into your eye. It is SO much brighter and more contrasty with still a 1 degree field. Here's what it looked like:

Trapezium, the fish mouth was far from dark and showed gas and dust throughout. De Mairan's (M43) had that distinctive bird's head shape and was bright, well defined and showed surface detail. The Running Man figure was visible if you knew what it looked like but the general nebulosity there was bright. Back on M42 the two wings sweeping out from the Trap were brilliant and smooth, and then I tried for my favourite. A hook of dusty gas emerges from a hole in one of the wings and looks lovely in images as it curles out. Well, the hole was really obvious and with averted vision I saw the hook for the first time. Glorious. Very happy bunny.

When the TEC140 has finished its present image (perhaps two more nights) the Nagler is going straight in the back for a visual night. Can't wait.

But I really must get some help and advice to get more out of the 20 inch. I have a classy professional optician coming in April so I will pick his considerable brains.

Olly

[michael.h.f.wilkinson]

Nice report. I'd love to get a look at M42 through a monster scope like that.

[nightfisher]

nice one olly, i had a peep at M42 tonight managed the trapezium in the tal100rs with 25mm tal plossl, then popped the 15mm plossl in and really got a good look

[John]

Nice report Olly and an interesting one in terms of the debates that we often have on the impact of an oversized exit pupil. Your experience seems to suggest that there is a tangible visual benefit to getting the exit pupil right

[michael.h.f.wilkinson]

Nice report Olly and an interesting one in terms of the debates that we often have on the impact of an oversized exit pupil. Your experience seems to suggest that there is a tangible visual benefit to getting the exit pupil right

Or you can just do the math: a 7 mm exit pupil for people with 5 mm pupils wastes about 50% of the light (25/49 is transmitted , excluding central obstruction effects). Its like moving from a 20" to a 14.3" with oversized central obstruction . Nobody doubts that a 20" sees more than a 14".

[ollypenrice]

Or you can just do the math: a 7 mm exit pupil for people with 5 mm pupils wastes about 50% of the light (25/49 is transmitted , excluding central obstruction effects). Its like moving from a 20" to a 14.3" with oversized central obstruction . Nobody doubts that a 20" sees more than a 14".

Yes and this was in exact accord with what I saw, a simply staggering gain in light grasp from the eyeball point of view.* I have had this experience before with some old 11x80 bins. Exit pupil too big, not anything like as bright as 15X70.

Olly

* A foolish phrase since a point of view from anything other than an eyeball would be difficult to obtain...

[John]

Or you can just do the math: a 7 mm exit pupil for people with 5 mm pupils wastes about 50% of the light (25/49 is transmitted , excluding central obstruction effects). Its like moving from a 20" to a 14.3" with oversized central obstruction . Nobody doubts that a 20" sees more than a 14".

Thanks for the reminder about the math Michael

Despite this, we have had debates on here that cast doubt over whether is a noticable difference visually and I've seen eyepieces that would deliver an oversize exit pupil reccommended on the basis that "you probably won't notice any difference".

I've always advocated and practiced the idea of maintaining optimum exit pupils (one of the reasons I shelled out for a Nagler 31mm) and it's good to read Olly's 1st hand experience confirming that this is something that should be an important consideration when choosing low power eyepieces for fast scopes

[michael.h.f.wilkinson]

I have used my Paragon 40 mm in the 80mm F/6, simply because I do not have the Nagler 31 T5 (yet), and also because I then do not need a finder scope (5.6 deg FOV). I do notice a distinct drop in brightness of objects when compared to using a 22mm Nagler. You need to see difference by direct comparison. If you just look through the scope with the Paragon inserted, everything looks fine, it is only when you compare it directly that you see the difference.

[Space Hopper]

Hi,

Just wondered how my stars you managed to see

in the trapezium, through the 20" ?

Thanks TB

[Guest]

Normally I would get the main 4 + E and F if the seeing is good through mine. I must admit I have not taken a chart out to have a look for the others. G might be OK but I think the H stars are hard. If you get lucky Olly try M42 with an Ethos 21 in the 20" :-)

Owen

[ollypenrice]

Normally I would get the main 4 + E and F if the seeing is good through mine. I must admit I have not taken a chart out to have a look for the others. G might be OK but I think the H stars are hard. If you get lucky Olly try M42 with an Ethos 21 in the 20" :-)

Owen

I will, Owen, if one turns up. In fact I was all set to buy one in the sales but couldn't find anyone who had them so I settled on the 26 Nagler and some change!

The optics on our 20 inch are of the Light Bucket variety so are grand for the Wow factor but lees good for starsplitting. I have an expert cooming soon and will discuss with him how to improve it. It is still pretty exciting though.

I'm itching to get the Nagler in the TEC but can't take out the camera yet because of the need to conserve flats.

O

[nightvision]

Sounds like a great visual expereince, Olly what focal length is the 20"?

I use a Nagler 17T4 in a 12" f5 dob and that delivers the wow factor on M42, knowing the FL of your 20" will certainly help me relate to the view you describe.

Tony.

[ollypenrice]

Sounds like a great visual expereince, Olly what focal length is the 20"?

I use a Nagler 17T4 in a 12" f5 dob and that delivers the wow factor on M42, knowing the FL of your 20" will certainly help me relate to the view you describe.

Tony.

Hi Tony, it's 2050mm.

Olly