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Eyepiece Comparisons with the 14mm Denkmeier (D14)


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Introduction

Denkmeier Optical eyepieces are available in 21mm and 14mm focal lengths, branded D21 and D14 respectively. These units were designed with high quality Denkmeier Binoviewers in mind but can also be purchased individually for use without a binocular viewer.

I was interested to explore the possibility of replacing my 13mm Nagler Type 6 with the D14 as I had received good feedback about this eyepiece, despite limited publicly available information. I bought a single D14 unit four months ago for cyclops mode viewing, and have since obtained other premium wide-fields on a temporary basis to enable this 13-14mm eyepiece comparison, as follows:

  • 14mm Pentax XW

  • 13mm Nagler Type 6

  • 13mm Ethos

A 16-inch f/4.4 David Lukehurst Dobsonian was used for this exercise, and the review was conducted from a totally independent standpoint. Although the main focus was the D14, I also purchased a D21 eyepiece and the same general conclusions apply.

14mm Denkmeier Eyepiece Specification

  • High index glass elements, fully multi-coated on all air-to-glass surfaces.

  • 1.25-inch barrel format

  • Apparent field of view of 65 degrees

  • Eye relief of 20mm

  • Rubber knurling for secure gripping

  • Black anodized aluminium housing, laser engraved with the Denkmeier logo

  • Rotating batwing rubber eye-guards

  • Current pricing of $578 for an eyepiece pair or $289 individually

  • Optional eyepiece vaults for safe storage

Performance Overview

The D14 provided sharp views to the edge of field without a coma corrector at f/4.4. Light throughput, sharpness and contrast were notably excellent qualities of this eyepiece. There did not appear to be any rectilinear distortion and there was no evidence of pincushion aberration. The eyepiece provided a very flat field, slightly larger than the currently marketed 65 degrees, and was particularly engaging in its view. Images appeared neutral white with no obvious lateral colour. As light scatter was also very minimal, the D14 can be considered well suited for planetary observation. The eyepiece performed particularly well with high quality Barlow lenses.

The unit is smaller and lighter than other eyepieces in similar (65-70 degree) categories at the current time. Eye relief seemed very generous and the winged eye-guard can be folded down to provide eyeglass wearers with a good degree of observing comfort.

14mm Denkmeier vs. 14mm Pentax XW

The 14mm Pentax XW eyepiece offers an apparent field of view of 70 degrees and 20mm eye relief.

Comparisons between D14 and 14XW eyepieces revealed similar on-axis performance levels from the perspective of sharpness, transmission and contrast. Apparent field of view sizes appeared comparable, with the D14 evidently providing in the region of 70 degrees despite being advertised as only a 65-degree eyepiece.

Although marketed with 20mm of eye relief, the D14 appeared to offer slightly less than the 14XW in this area, most likely explained by the recessed top lens on the D14. Both eyepieces should be fine for the majority of people wearing eyeglasses.

Off-axis views through the D14 were noticeably superior because of minor field curvature visible in the 14mm Pentax XW at f/4.4 in a 16-inch Newtonian. The 14XW required a Paracorr to eliminate the effects of this aberration. The D14, with its very flat field, proved more effective for viewing open clusters and star fields. From a purely personal perspective, it has provided some of the best views of M11 ever observed and is a favorite eyepiece for such objects.

It was difficult to decide which ocular proved the most effective for viewing galaxies, although it was clear that each excelled in this area. Both eyepieces generated very high contrast images and detailed views of larger galaxies, and were equally effective for detecting objects at the threshold of visibility. However, an eyepiece exit pupil size of 3.2mm with my telescope was considered rather large; a decreasing range from 2.5mm to 1.6mm would have been more preferable for the majority of galaxies but Denkmeier Optical do not currently offer a focal length shorter than 14mm.

Both eyepieces yielded high contrast images of Jupiter with similar detail, colour rendition and low levels of light scatter as worthy planetary contenders.

On certain occasions whilst observing the deep sky, there was a perception that the images in the D14 appeared marginally whiter and brighter than in the 14XW. However, opportunities for observing with the 14XW were rather limited to be absolutely certain about this.

At 9oz in weight, the D14 is certainly considerably lighter and indeed smaller than the 14XW.

Overall, the verdict would need to be given in favor of the D14, based on better off-axis performance, compactness and slightly more natural & refreshing views.

14mm Denkmeier vs. 13mm Nagler Type 6

The 13mm Nagler Type 6 sports an apparent field of view of 82 degrees and 12mm eye relief.

The 13T6 provided well-corrected, high contrast and sharp views. It is clearly a very good eyepiece that I have enjoyed using over recent years. The off-axis views without a coma corrector were better than those produced by the 14XW and quite similar to the D14 over 70-degrees of evidently flat field.

On-axis, there was a marginal difference in transmission and contrast in favor of the D14 but the 13T6 offered the largest apparent field of view. However, the small eye-lens and shorter eye relief of the 13T6 limited its potential to easily take advantage of the full 82 degrees. Thus, the difference in field of view between the two eyepieces was not as significant as one might initially expect, and the D14 was certainly very engaging in this regard. The longer eye relief of the D14 also enabled more comfortable viewing.

I enjoyed using the D14 on globular clusters and found that the transparency of the eyepiece enabled slightly more stars to be resolved in showpiece objects such as M13.

On Jupiter there was a very small amount of additional light scatter through the 13T6, in addition to a less neutral white image because of the inherent coffee tone of the Nagler, but it still delivered a very nice view of the planet.

The true field of view of the D14 appeared slightly larger than the 13T6 and 14XW, each advertised with a field stop diameter of 17.6mm. The D14 was estimated to be approximately 17.9mm in this respect.

The 13T6 is even smaller and lighter than the D14, representing the most compact wide-field unit considered in this review.

Generally, the D14 delivered a remarkably natural view, while the warm colour tone of the 13T6 seemed to create the opposite effect. The D14 also provided a darker background.

Again, I would have to give the edge to the D14.

14mm Denkmeier vs. 13mm Ethos

The 13mm Ethos provides a huge apparent field of view of 100 degrees and sufficient eye relief of 15mm for non-eyeglass wearers.

With its incredible 100-degree field, the 13E is a very spectacular eyepiece and a great marvel in modern eyepiece engineering. The 13E provided slightly improved optical performance over the 13T6 in my opinion, e.g., the Ethos performed better on globular clusters and was a match for the D14 in this regard.

On-axis and off-axis (to about the 70 degrees of the D14), the views between the D14 and 13E were fairly comparable in terms of transmission and sharpness. The D14 provided the most natural views although the 13E was noticeably more colour neutral than the 13T6. The D14 also provided a slightly darker background.

On certain objects the D14 produced slightly superior images, e.g., the Veil nebula displayed marginally greater contrast and definition despite the view through the 13E being delivered at a slightly higher magnification. I also liked the way the D14 seemed better at emphasizing natural star colours, a very beneficial feature for observing star fields, open clusters and double stars. Colours were also more visibly rendered in planetary nebulae such as M57. It should be stated that such differences were quite subtle, but nevertheless clearly visible, at least to my eyes. Both eyepieces produced very sharp images but the D14 demonstrated a certain unique crispness - a subjective quality that is difficult to convey.

In some areas the 13E performed better than the D14, e.g., it generated slightly more colourful and somewhat more pleasing images of Jupiter (possibly because of the warmer tone of the Ethos), although the light scatter was in the same order i.e., very minimal.

The field of the view through the 13E appeared enormous in comparison with the D14. Astronomers seeking the ultimate in virtual spacewalk observing would most likely prefer the 13E in this respect. I find that 70 degrees is more than adequate for most of my needs, and in many cases I use narrow field eyepieces such as TMB Supermonos when observing deep sky objects.

The 13E is a much larger and heavier eyepiece than the D14, tradeoffs that were obviously necessary to ensure the highly expansive and impressive field of the Ethos.

In terms of preferences, I would place the D14 narrowly ahead of the 13E in what was the closest of all the comparisons in this review.

Summary of Comparisons

The table below outlines the results for each eyepiece against assessment criteria in the left-hand column with equal weightings applied. Based on these scores, the overall ranked winner is the 14mm Denkmeier followed closely by the 13mm Ethos and the 14mm Pentax XW.

Eyepiece Criteria

D14

14XW

13T6

13E

Sharpness

*****

*****

****/*

*****

Transmission

*****

*****

****

*****

Contrast

*****

*****

****

****/*

Off-axis Sharpness

****

**

****

****

Field of View

***

***

****

*****

Eye Relief

****

*****

**

***

Colour Fidelity

*****

****

***

****

Background Darkness

*****

****

***

****

Accuracy of Image

*****

****

***

****

Scatter Control

****

****

***

****

Ergonomics

****

***

*****

**

Overall Ranking

1

3

4

2

Table 1: Summary of Results

Conclusion

The 14mm Denkmeier is an absolutely outstanding wide-field eyepiece that is very hard to fault in any way.

The D14 produces what I would consider to be truly “orthoscopic” views from the perspective of natural and correct image representation rather than eyepiece design. Combining refreshingly crisp, high contrast and pristine images against dark sky backgrounds, the 14mm Denkmeier provides some truly breathtaking views. Such intrinsic characteristics are difficult to find in other wide field designs. If these are qualities that other observers also value, then the D14 would be an excellent choice in the 13-14mm wide-field category – very highly recommended.


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